Chemical Foundations:

Elements, Atoms and Ions

Lectures 3, 4, 5

Chem 101

112 elements are known

88* elements are found in nature; on earth, in the

oceans and atmosphere The most abundant elements

Element Mass Percent Oxygen 49.2

Silicon 25.7

Aluminum 7.50

Iron 4.71

Calcium 3.39

Sodium 2.63

Potassium 2.40

Magnesium 1.93

Hydrogen 0.87

Titanium 0.58

Chlorine 0.19

Phosphorus 0.11

Manganese 0.09

Carbon 0.08

Sulfur 0.06

Barium 0.04

Nitrogen 0.03

Fluorine 0.03

All others 0.49

Elements of Life

Some elements are used in their compound

forms rather than as a pure element

Hmco Photo File

Compare the Earth’s Crust to the

Human Body

Footprints in the sand

of the Namib Desert in Namibia.

Getty Images (Royalty Free)

Dalton’s Atomic Theory

• Elements are composed of tiny particles

called atoms.

– All atoms of a given element are identical. – All carbon atoms have the same chemical and physical

properties.

– Atoms of a given element are different from

those of any other element. – Carbon atoms have different chemical and physical

properties than sulfur atoms.

Elements

Dalton pictured compounds as collections of atoms.

NO, NO2, and N2O are represented here.

Atoms of different elements combine to

form compounds.

Dalton’s Atomic Theory

• Law of Constant Composition: – all samples of a compound contain the same

proportions (by mass) of the elements that form the compound.

• Atoms are indivisible by chemical processes. – All atoms present at beginning are present at the

end.

– Atoms are not created or destroyed, just rearranged in chemical reactions.

– Atoms of one element cannot change into atoms of another element.

• Cannot turn lead into gold by a chemical reaction

Formulas of Compounds

• NaCl Each element is represented by its 1 or 2 letter symbol.

• H2O The number of each type of atom is indicated by a subscript written to the right of the element symbol. If only one atom is present, do not include a subscript.

• Mg(NO3)2 If polyatomic groups are present in the molecule, they are written inside parentheses if more than one group is present.

• KNO3 If only 1 polyatomic group, no parentheses

Rutherford’s Nuclear Model • The atom contains a tiny

dense center called the nucleus.

– The volume is about 1/10 trillionth the volume of the atom.

• The nucleus is essentially the entire mass of the atom.

• The nucleus is positively charged.

– The amount of positive charge of the nucleus balances the negative charge of the electrons.

• The electrons move around in the empty space of the atom surrounding the nucleus.

The Modern Atom • Atoms are composed of three

main pieces: protons, neutrons,

and electrons.

• The nucleus contains protons and

neutrons.

• The electrons move around the

space outside the nucleus.

• The protons have a charge of +1

• The neutrons have a charge of 0

• The electrons have a charge of -1

Lithium Atom

The Elements

Classified as Metals and as Nonmetals.

Elements are arranged in a pattern

called the periodic table

Position on the table allows us to

predict properties of the element

Elements • Metals

– Lustrous, malleable,

ductile, conduct heat and

electricity

• Nonmetals – Dull, brittle, insulators

• Metalloids – Also called semi-metals

– Some properties of both metals & nonmetals

Gold Au

Platinum Pt

Sulfur S

Boron

Elements on the Modern Periodic Table

The A columns

are Main Group

Elements or

Families

Elements with

similar chemical

and physical

properties are in

the same column

Transition elements

Inner transition

elements

Rare earth

Periods are rows

Natural States of Elements

• Gases:

– monoatomic gases such as noble gases

– diatomic gases such as O2

• Liquids such as Hg or Br2

• Solids such as metals or carbon or sulfur S8

Because these elements all show similar chemical behavior,

they are listed vertically in the periodic table, as a "family" of

elements.

Halogens

All the elemental forms of the Group 7

elements contain diatomic molecules.

The noble gases: Group 8 of the periodic

table.

Non reactive

Argon gas consists

of a collection of separate argon atoms.

Gaseous nitrogen and oxygen contain

diatomic (two-atom) molecules.

The decomposition of 2 water molecules (H2O) to form two

hydrogen molecules (H2) and an oxygen molecule (O2)

Graphite and diamond,

two forms of carbon.

Fundamental Photographs

Some elements can

exist in different

elemental structures.

The three solid

elemental forms of carbon (allotropes):

(a) diamond, (b) graphite, and (c) buckminsterfullerene.

C60

Neutral sodium atom (Na).

There are 11

protons in the

nucleus for a

charge of 11+

The number of

neutrons in the

nucleus does not

affect the charge

Neutral sodium atom

(Na) and sodium ion (Na+).

What noble gas has 10 electrons?

Neutral magnesium atom

(Mg) and magnesium ion (Mg2+).

What noble gas has 10 electrons?

Neutral aluminum atom

(Al) and aluminum ion (Al3+).

What noble gas has 10 electrons?

Atomic Structures of Ions: Cations

• Metals form cations.

• For each positive charge the ion has 1

less electron than the neutral atom. – Na = 11 e-, Na+ = 10 e-

– Ca = 20 e-, Ca+2 = 18 e-

• Cations are named the same as the

metal

sodium Na Na+ + 1e- sodium ion

calcium Ca Ca+2 + 2e- calcium ion

Neutral chlorine atom

(Cl) and chloride ion (Cl-).

What noble gas has 18 electrons?

Atomic Structures of Ions: Anions

• Nonmetals form anions.

• For each negative charge the ion has 1

more electron than the neutral atom. – F = 9 e-, F- = 10 e-

– P = 15 e-, P3- = 18 e-

• Anions are named by changing the

ending

of the name to -ide – Fluorine F + 1e- F- fluoride ion

– Oxygen O + 2e- O2- oxide ion

Ions • Cations: ions that have a positive charge

– Form when an atom loses electrons

• Anions: ions that have a negative charge

– Form when an atom gains electrons

• Ions with opposite charges attract

– Cations and anions attract each other

• Compounds must have no total charge,

balance the numbers of cations and anions in a

compound to get 0 total charge.

Ionic Charges and Compounds Charges on the ions of some

elements can be predicted from

the periodic table.

Cations and anions usually form

simultaneously to form ionic compounds

Solid sodium chloride

highly magnified.

Color-Pic, Inc.

Sodium metal (left) and chlorine gas.

Hmco Photo File.

The arrangement of sodium ions (Na+) and chloride ions

(Cl-) in the ionic compound sodium chloride.

When ionic substances dissolve in

water they conduct electricity.

Moving ions conduct electricity.

NaCl:

Each sodium ion has a 1+ charge

Each chloride ion has a 1- charge,

They must occur in equal numbers to give a net charge of zero.

Formula of Ionic Compounds

MgCl2: To balance the 2+ charge on Mg2+, two

Cl- ions are necessary to give a net charge of zero.

Formula of Ionic Compounds

Isotopes

• All atoms of an element have the same

number of protons.

• The number of protons in an atom of a given

element is the same as the atomic number.

– Found on the periodic table

• Atoms of an element with different numbers of

neutrons are called isotopes.

Two isotopes of sodium.

23Na 24Na

18Na to 35Na

Isotopes • All isotopes of an element are chemically identical.

– Undergo the exact same chemical reactions

• Isotopes of an element have different masses.

• Isotopes are identified by their mass numbers.

– Mass number = # protons + # neutrons

• How are isotopes formed? – Isotopes are either primordial, or are formed via the decay of heavier

mass radioactive elements. for example, U235 and U238 mined from the earth are primordial (formed in supernova explosions over the course of the billions of years before earth coalesced). They can also be synthesized in the atmosphere and in reactor or accelerator facilities, by processes such as fusion and fission.