ch 5 notes

Elements, Atoms, and

Ions

The Language of The Language of ChemistryChemistryThe Language of The Language of ChemistryChemistry

• CHEMICAL ELEMENTSCHEMICAL ELEMENTS - - – pure substances that cannot be decomposed by pure substances that cannot be decomposed by

ordinary means to other substances.ordinary means to other substances.

SodiumBromine

Aluminum

The Language of The Language of ChemistryChemistryThe Language of The Language of ChemistryChemistry

• The elements, The elements, their names, and their names, and symbols are given symbols are given on theon the PERIODIC PERIODIC TABLETABLE

• How many How many elements are elements are there?there?

The Periodic TableThe Periodic Table

Dmitri Mendeleev (1834 - 1907)Dmitri Mendeleev (1834 - 1907)

An atom consists of aAn atom consists of a

• nucleusnucleus

– (of (of protonsprotons and and neutronsneutrons) )

• electronselectrons in space about the nucleus. in space about the nucleus.

The The AtomAtom

NucleusNucleus

Electron cloudElectron cloud

http://www.youtube.com/watch?v=kypne21A0R4

http://www.youtube.com/watch?v=qmgE0w6E6ZI&mode=related&search=

Copper Copper atoms on atoms on silica silica surface.surface.

• An An atomatom is the smallest particle of an is the smallest particle of an element that has the chemical element that has the chemical properties of the element.properties of the element.

Distance across = 1.8 nanometer (1.8 x 10-9 m)

Compounds

– composed of 2 or more elements in a fixed ratio

– properties differ from those of individual elements

– EX: table salt (NaCl)

AA MOLECULEMOLECULE is the smallest unit of is the smallest unit of a compound that retains the chemical a compound that retains the chemical characteristics of the compound.characteristics of the compound.

Composition of molecules is given by aComposition of molecules is given by a

MOLECULAR FORMULAMOLECULAR FORMULA

HH22OO CC88HH1010NN44OO22 - caffeine - caffeine

ELEMENTS THAT EXIST AS ELEMENTS THAT EXIST AS DIATOMICDIATOMIC MOLECULES MOLECULES

ELEMENTS THAT EXIST AS ELEMENTS THAT EXIST AS DIATOMICDIATOMIC MOLECULES MOLECULES

Remember:

BrINClHOF

These elements only exist as

PAIRS. Note that when they

combine to make compounds, they

are no longer elements so they are no longer in

pairs!

Where Did it All Begin?

• The word “atom” comes from the Greek word “atomos” which means indivisible.

• The idea that all matter is made up of atoms was first proposed by the Greek philosopher Democritus in the 5th century B.C.

Dalton’s Atomic Theory

John Dalton (1766-1844) proposed an atomic theory

While this theory was not completely correct, it revolutionized how chemists looked at matter and brought about chemistry as we know it today instead of alchemy

Thus, it’s an important landmark in the history of science.

Dalton’s Atomic Theory - Summary

1. matter is composed, indivisible particles (atoms)2. all atoms of a particular element are identical3. different elements have different atoms4. atoms combine in certain whole-number ratios 5. In a chemical reaction, atoms are merely

rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.

Problems with Dalton’s Atomic Theory?1. matter is composed, indivisible particles

Atoms Can Be Divided, but only in a nuclear reaction2. all atoms of a particular element are identical

Does Not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)!

3. different elements have different atomsYES!

4. atoms combine in certain whole-number ratiosYES! Called the Law of Definite Proportions

5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.Yes, except for nuclear reactions that can change atoms of one element to a different element

• J.J. Thompson discovered electrons in 1897 by performing the cathode ray

experiment.

Plum Pudding ModelCathode Ray tube

What about Electrons?

• Much of Dalton’s theories are accepted except that atoms are known now to be divisible into sub-particles.

• Robert A. Millikin 1868-1953 carried out experiments to discover the charge and mass of electrons by

• Physicist James Chadwick 1891-1974 confirmed the existence of yet another subatomic particle: the neutron

Millikin Oil Drop experiment

Rutherford’s experiment.

Ernest Rutherford wondered how all these particles were put together

The modern view of the atom was developed by The modern view of the atom was developed by Ernest RutherfordErnest Rutherford (1871-1937). (1871-1937).

Results of foil

experiment if Plum

Pudding model had

been correct.

What Actually Happened

Niels Bohr

• Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum.

• This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit.

Niels Bohr

ATOM ATOM COMPOSITIONCOMPOSITION

•protons and neutrons in protons and neutrons in the nucleus.the nucleus.

•the number of electrons is equal to the the number of electrons is equal to the number of protons.number of protons.

•electrons in space around the nucleus.electrons in space around the nucleus.

•extremely small. One teaspoon of water has extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean 3 times as many atoms as the Atlantic Ocean has teaspoons of water.has teaspoons of water.

The atom is mostlyThe atom is mostlyempty spaceempty space

ATOMIC COMPOSITIONATOMIC COMPOSITION• Protons (pProtons (p++))

– + electrical charge+ electrical charge

– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g

– relative mass = 1.007 atomic relative mass = 1.007 atomic mass units mass units (amu) (amu) but we can round to 1but we can round to 1

• Electrons (eElectrons (e--))– negative electrical chargenegative electrical charge

– relative mass = 0.0005 amu relative mass = 0.0005 amu but we can round to 0but we can round to 0

• Neutrons (nNeutrons (noo))– no electrical chargeno electrical charge

– mass = 1.009 amu mass = 1.009 amu but we can round to 1but we can round to 1

Atomic Number, ZAtomic Number, Z

All atoms of the same element All atoms of the same element have the same number of have the same number of protons in the nucleus, protons in the nucleus, ZZ

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

AVERAGE Atomic MassAVERAGE Atomic Mass

Mass Number, AMass Number, A• C atom with 6 protons and 6 neutrons C atom with 6 protons and 6 neutrons

is the mass standard is the mass standard • = 12 atomic mass units= 12 atomic mass units• Mass NumberMass Number (A) (A)

= # protons + # neutrons= # protons + # neutrons• NOT on the periodic table…(it is the NOT on the periodic table…(it is the

AVERAGE atomic mass on the table)AVERAGE atomic mass on the table)• A boron atom can have A boron atom can have

A = 5 p + 5 n = 10 amuA = 5 p + 5 n = 10 amu

A

Z

10

5B

A

Z

10

5B

IsotopesIsotopes

• Atoms of the same element (same Z) Atoms of the same element (same Z) but different mass number (A).but different mass number (A).

• Boron-10 (Boron-10 (1010B) has 5 p and 5 nB) has 5 p and 5 n

• Boron-11 (Boron-11 (1111B) has 5 p and 6 nB) has 5 p and 6 n

10B

11B

Figure 3.10: Two isotopes of sodium.

Isotopes Isotopes & Their & Their

UsesUsesBone scans with Bone scans with radioactive radioactive technetium-99. technetium-99.

Isotopes & Their Isotopes & Their UsesUses

The The tritiumtritium content of ground water is content of ground water is used to discover the source of the water, used to discover the source of the water, for example, in municipal water or the for example, in municipal water or the source of the steam from a volcano. source of the steam from a volcano.

Atomic Symbols

Show the name of the element, a hyphen, and

the mass number in hyphen notation

sodium-23

Show the mass number and atomic number

in nuclear symbol formmass number 23 Na

atomic number 11

Isotopes?

Which of the following represent isotopes of the same element? Which element?

234 X 234

X235

X238

X

92 93 92 92

Answer:

234 U

234 Np

235 U

238 U

92 93 92 92

234 Np is not an isotope of Uranium.

93

Counting Protons, Neutrons, and Electrons

• Protons: Atomic Number (from periodic table)• Neutrons: Mass Number minus the number of protons

(mass number is protons and neutrons because the mass of electrons is negligible)

• Electrons: – If it’s an atom, the protons and electrons must be

the SAME so that it is has a net charge of zero (equal numbers of + and -)

– If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

Learning Check – Counting

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p+ _______ _______ _______

#no _______ _______ _______

#e- _______ _______ _______

Answers

12C 13C 14C 6 6 6

#p+ 6 6 6

#no 6 7 8

#e- 6 6 6

Learning Check

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is

1) 34X 2) 34X 3) 36X 16 14 14

Solution

An atom has 14 protons and 20 neutrons.A. It has atomic number

1) 14

B. It has a mass number of3) 34

C. The element is1) Si

D. Another isotope of this element would be

3) 36X 14

IONS IONS

• IONSIONS are atoms or groups of atoms with a positive or negative are atoms or groups of atoms with a positive or negative

charge. charge.

• Taking awayTaking away an electron from an atom gives a an electron from an atom gives a CATIONCATION with a with a

positive chargepositive charge

• AddingAdding an electron to an atom gives an an electron to an atom gives an ANIONANION with a with a

negative chargenegative charge..

• To tell the difference between an atom and an ion, look to see if To tell the difference between an atom and an ion, look to see if

there is a charge in the superscript! Examples: Nathere is a charge in the superscript! Examples: Na++ Ca Ca+2+2 I I-- O O-2-2

Na Ca I ONa Ca I O

Forming Cations & Forming Cations & AnionsAnions

Forming Cations & Forming Cations & AnionsAnions

A A CATIONCATION forms forms when an when an atom atom losesloses one or one or more electrons.more electrons.

An An ANIONANION forms forms when an when an atom atom gainsgains one or one or more electronsmore electrons

Mg --> Mg2+ + 2 e- F + e- --> F-

PREDICTING ION CHARGESPREDICTING ION CHARGESPREDICTING ION CHARGESPREDICTING ION CHARGES

In generalIn general

• metalsmetals (Mg) (Mg) lose electrons lose electrons ---> ---> cationscations

• nonmetalsnonmetals (F) (F) gain electronsgain electrons ---> ---> anionsanions

Charges on Common Charges on Common IonsIons

Charges on Common Charges on Common IonsIons

+3

-4 -1-2-3+1

+2

By losing or gaining e-, atom has same By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.number of e-’s as nearest Group 8A atom.

http://www.youtube.com/watch?v=IpaEGhjpZgc

Learning Check – Counting

State the number of protons, neutrons, and electrons in each of these ions.

39 K+ 16O -2 41Ca +2

19 8 20

#p+ ______ ______ _______

#no ______ ______ _______

#e- ______ ______ _______

Learning Check – Counting

State the number of protons, neutrons, and electrons in each of these ions.

39 K+ 16O -2 41Ca +2

19 8 20

#P 19 8 20

#N 20 8 21

#E 18 10 18

One Last Learning Check

Write the nuclear symbol form for the following atoms or ions:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 46 e- ___________

Answers

Write the nuclear symbol form for the following atoms or ions:

A. 8 p+, 8 n, 8 e- 16O 8

B. 17p+, 20n, 17e- 37Cl17

C. 47p+, 60 n, 46 e- 107Ag+

47

AVERAGE AVERAGE ATOMIC ATOMIC MASSMASS

• Because of the existence of isotopes, the Because of the existence of isotopes, the mass of a collection of atoms has an average mass of a collection of atoms has an average value.value.

• Boron is 20% Boron is 20% 1010B and 80% B and 80% 1111B. That is, B. That is, 1111B is B is 80 percent abundant on earth. 80 percent abundant on earth.

• For boron atomic weightFor boron atomic weight

= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

10B

11B

Isotopes & Average Atomic Isotopes & Average Atomic MassMass

• Because of the existence of isotopes, the mass Because of the existence of isotopes, the mass of a collection of atoms has an average value.of a collection of atoms has an average value.

• 66Li = 7.5% abundant and Li = 7.5% abundant and 77Li = 92.5%Li = 92.5%

–Avg. Atomic mass of Li = ______________Avg. Atomic mass of Li = ______________

• 2828Si = 92.23%, Si = 92.23%, 2929Si = 4.67%, Si = 4.67%, 3030Si = 3.10%Si = 3.10%

–Avg. Atomic mass of Si = ______________Avg. Atomic mass of Si = ______________

The Periodic Table

PeriodsPeriods in the Periodic in the Periodic TableTable

GroupsGroups in the Periodic in the Periodic TableTable

Elements in groups react in similar ways!

Regions of the Periodic Regions of the Periodic TableTable

University of North Texas Chemistry BuildingThe only full periodic table with all the elements (except man-made) in existence

Group 1A: Alkali MetalsGroup 1A: Alkali MetalsGroup 1A: Alkali MetalsGroup 1A: Alkali Metals

Cutting sodium metalCutting sodium metal

Reaction of potassium + H2O

MagnesiumMagnesium

Magnesium Magnesium oxideoxide

Group 2A: Alkaline Earth MetalsGroup 2A: Alkaline Earth Metals

Group 7A: The Halogens Group 7A: The Halogens (salt makers) (salt makers) F, Cl, Br, I, AtF, Cl, Br, I, At

Group 7A: The Halogens Group 7A: The Halogens (salt makers) (salt makers) F, Cl, Br, I, AtF, Cl, Br, I, At

Group 8A: The Noble Group 8A: The Noble (Inert) Gases(Inert) Gases

He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn

Group 8A: The Noble Group 8A: The Noble (Inert) Gases(Inert) Gases

He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn• Lighter than air

balloons

• “Neon” signs

• Very Unreactive because they have full electron levels

XeOFXeOF44XeOFXeOF44

Transition ElementsTransition ElementsTransition ElementsTransition Elements

Lanthanides and actinidesLanthanides and actinides

Iron in air gives Iron in air gives iron(III) oxideiron(III) oxide

• But Why Does The Periodic Table end too quickly? Can’t we just add a proton to the end???

• Let’s Watch!

Chemistry of Groups

• Group 1: Alkali Metals

• Group 2: Alkaline Earth Metals

• Groups 3-11: Transition Elements

• Group 17: Halogens

• Group 18: Noble Gases

• Diatomic Molecules

Group 1: Alkali Metals

• Most active metals, only found in compounds in nature

• React violently with water to form hydrogen gas and a strong base: 2 Na (s) + H2O (l) 2 NaOH (aq) + H2 (g)

• 1 valence electron

• Form +1 ion by losing that valence electron

• Form oxides like Na2O, Li2O, K2O

Alkali Metals

• The alkali metals, found in group 1 of the periodic table (formerly known as group IA), are very reactive metals that do not occur freely in nature. These metals have only one electron in their outer shell. Therefore, they are ready to lose that one electron in ionic bonding with other elements.

• As with all metals, the alkali metals are malleable, ductile, and are good conductors of heat and electricity. The alkali metals are softer than most other metals.

• Cesium and francium are the most reactive elements in this group. Alkali metals can explode if they are exposed to water.

Group 2: Alkaline Earth Metals

• Very active metals, only found in compounds in nature

• React strongly with water to form hydrogen gas and a base:

–Ca (s) + 2 H2O (l) Ca(OH)2 (aq) + H2 (g)

• 2 valence electrons

• Form +2 ion by losing those valence electrons

• Form oxides like CaO, MgO, BaO

Alkaline Earth

• The alkaline earth elements are metallic elements found in the second group of the periodic table. All alkaline earth elements have an oxidation number of +2, making them very reactive.

• Because of their reactivity, the alkaline metals are not found free in nature.

Groups 3-12: Transition Metals

• Many can form different possible charges of ions

• If there is more than one ion listed, give the charge as a Roman numeral after the name

• Cu+1 = copper (I) Cu+2 = copper (II)

• Compounds containing these metals can be colored.

Transition Metals

• The 38 elements in groups 3 through 12 of the periodic table are called "transition metals". As with all metals, the transition elements are both ductile and malleable, and conduct electricity and heat.

• The interesting thing about transition metals is that their valence electrons, or the electrons they use to combine with other elements, are present in more than one shell. This is the reason why they often exhibit several common oxidation states.

• There are three noteworthy elements in the transition metals family. These elements are iron, cobalt, and nickel, and they are the only elements known to produce a magnetic field.

Group 17: Halogens

• Most reactive nonmetals

• React violently with metal atoms to form halide compounds: 2 Na + Cl2 2 NaCl

• Only found in compounds in nature

• Have 7 valence electrons

• Gain 1 valence electron from a metal to form -1 ions

• Share 1 valence electron with another nonmetal atom to form one covalent bond.

Halogens• The halogens are five non-metallic

elements found in group 7 of the periodic table. The term "halogen" means "salt-former" and compounds containing halogens are called "salts". All halogens have 7 electrons in their outer shells, giving them an oxidation number of -1. The halogens exist, at room temperature, in all three states of matter:

• Solid- Iodine, Astatine • Liquid- Bromine • Gas- Fluorine, Chlorine

Group 18: Noble Gases

• Are completely nonreactive since they have eight valence electrons, making a stable octet.

• Kr and Xe can be forced, in the laboratory, to give up some valence electrons to react with fluorine.

• Since noble gases do not naturally bond to any other elements, one atom of noble gas is considered to be a molecule of noble gas. This is called a monatomic molecule. Ne represents an atom of Ne and a molecule of Ne.

Noble Gases

• The six noble gases are found in group 18 of the periodic table. These elements were considered to be inert gases until the 1960's, because their oxidation number of 0 prevents the noble gases from forming compounds readily.

• All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable.

Diatomic Molecules

• Br, I, N, Cl, H, O and F are so reactive that they exist in a more chemically stable state when they covalently bond with another atom of their own element to make two-atom, or diatomic molecules.

• Br2, I2, N2, Cl2, H2, O2 and F2

• The decomposition of water: 2 H2O 2 H2 + O2

Electronegativity• An atom’s attraction to electrons in a chemical bond.

• F has the highest, at 4.0

• Fr has the lowest, at 0.7

• If two atoms that are different in EN (END) from each other by 1.7 or more collide and bond (like a metal atom and a nonmetal atom), the one with the higher electronegativity will pull the valence electrons away from the atom with the lower electronegativity to form a (-) ion. The atom that was stripped of its valence electrons forms a (+) ion.

• If the two atoms have an END of less than 1.7, they will share their unpaired valence electrons…covalent bond!

Ionization Energy

• The energy required to remove the most loosely held valence electron from an atom in the gas phase.

• High electronegativity means high ionization energy because if an atom is more attracted to electrons, it will take more energy to remove those electrons.

• Metals have low ionization energy. They lose electrons easily to form (+) charged ions.

• Nonmetals have high ionization energy but high electronegativity. They gain electrons easily to form (-) charged ions when reacted with metals, or share unpaired valence electrons with other nonmetal atoms.

Ions• Ions are charged particles formed by the gain or

loss of electrons.

– Metals lose electrons (oxidation) to form (+) charged cations.

– Nonmetals gain electrons (reduction) to form (-) charged anions.

• Atoms will gain or lose electrons in such a way that they end up with 8 valence electrons (stable octet).

– The exceptions to this are H, Li, Be and B, which are not large enough to support 8 valence electrons. They must be satisfied with 2 (Li, Be, B) or 0 (H).

New Chemical Element• Recent hurricanes and gasoline issues are proof of the existence of

a new chemical element. Research has led to the discovery of the heaviest element yet known to science. The new element, Governmentium (Gv), has one neutron, 25 assistant neutrons, 88 deputy neutrons, and 198 assistant deputy neutrons, giving it an atomic mass of 312. 

• These 312 particles are held together by forces called morons, which are surrounded by vast quantities of lepton-like particles called peons. Since Governmentium has no electrons, it is inert; however, it can be detected, because it impedes every reaction with which it comes into contact.  

• A minute amount of Governmentium can cause a reaction that would normally take less than a second to take from four days to four years to complete. Governmentium has a normal half-life of 2- 6 years; It does not decay, but instead undergoes a reorganization in which a portion of the assistant neutrons and deputy neutrons exchange places. In fact, Governmentium's Mass will actually increase over time, since each reorganization will cause more morons to become neutrons, forming isodopes. This characteristic of moron promotion leads some scientists to believe that Governmentium is formed whenever morons reach a critical concentration. This hypothetical quantity is referred to as critical morass.

• When catalyzed with money, Governmentium becomes Administratium, an element that radiates just as much energy as Governmentium since it has half as many peons but twice as many morons.

• Isn't Science Wonderful!!!!!!

Now You Should Be Able To…

• Analyze stable and unstable isotopes of an element

to determine the relationship between the isotope’s

stability and it application.

• Describe similarities and differences of isotopes of

elements

• Give examples of uses of isotopes in everyday life

• Carbon-12 and its isotopes

• Unstable isotopes are radioactive

• Isotopes of hydrogen

• Define stable and unstable

Now You Should Be Able To…Describe the physical and chemical characteristics ofan element using the periodic table and makeinferences about its chemical behavior.

Characteristics:• Metal, nonmetal, metalloid• Reactivity• Valence electrons• Solid, liquid, gas• Oxidation number• Electronegativity/ Electron affinity

Periodic Table:Names: Inner transitions, noble gases, transition

metals, halogens, alkali metals, alkalineearth metals

• Groups and periods• Predict properties of elements based on the

element’s position on the periodic table