atomic concepts power point 1011

8/6/2019 Atomic Concepts Power Point 1011

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AtomicAtomic

ConceptsConcepts

Unit 3:


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What is an atom?What is an atom?

y The smallest particle ofan element that

retains the properties of that element.

Individualatoms can be

seen using what is called

a scanning, tunneling

microscope (invented

1981.) This is an image is

of gold atoms.


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John DaltonJohn Dalton18031803


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Daltons Theory Cont.Daltons Theory Cont.y 3. Atoms of different elements can_______________________ or can

___________________ with one another in

simple whole-numberratios to formcompounds (law of constant composition)

y

4. ___________________ occur when atomsare separated, joined, orrearranged. Atoms of

one element can _____________ ________

into atoms ofanother element as aresult ofa

chemicalreaction.

physically mix togetherchemically combine

Chemical reactions

never be changed


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Daltons Model (1803)Daltons Model (1803)


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A penny contains 2.4 x 1022

copper atoms.

There are 6.95 x 109 peopleon Earth.

Thats a lot of atoms!


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The Subatomic ParticlesThe Subatomic Particles

y Electrons - ___________________________________________________

Charge ____

Mass (amu) ________

Mass (grams) ____________

Are negatively chargedsubatomic particles

-1 1

1840 amu

9.11 x 10-28

g


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Cathode RayTubeCathode RayTube

y

Cathode RayVideo


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y Protons - ________________________

________________________________

Charge ______________

Mass (amu) ______________Mass (grams) ______________

Are positively charged

subatomic particles

+1

11.67 x 10-24g


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y eutrons - ______________________

________________________________

Charge ______________

Mass (amu) ______________

Mass (grams) ______________

subatomic particles with

no charge. Found in nucleus

0

1

1.67 x 10-24

g


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y A typicalatomic radius is about 100pm,

whereas the radius ofan atomic nucleus is

about 5 x 10-3pm Imagine that in an atomwere the size of the Houston Astrodome, the

volume of its nucleus would be comparable to

that ofa small marble.


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y ucleus - ________________________

_________________________________________

Central core of an atom

composed of protons and neutrons


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ohr modelBohr model Planetary ModelPlanetary Model


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Modern TheoryModern Theory

y In the modern theory (the wave-mechanical model) electrons are

considered to be found in an area of

probability known as electron clouds.


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Atomic StructureAtomic Structurey

Atomic Number - ___________________________________________________

The elements on the periodic table arearranged according to atomic number.

The atomic number identifies the element.

Since atoms are electrically neutral: the # of

__________ in the nucleus ofan atom

=the number of __________ outside the

nucleus

The number ofprotons in the nucleus of an atom

protonselectrons


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y Mass number - ____________________

_________________________________

Nuclear symbol: Used to represent the

composition ofan atom in shorthandnotation, the symbol of the element with

two additional numbers to the left are used.

Sum of the number of

protons and neutrons a whole #


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Nuclear SymbolNuclear Symbol

y The _________ number is written as thesubscript and the _______ number is

written as the superscript.

Heatomic

2

mass

4


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OtherrepresentationsOtherrepresentations

y Helium 4

y He 4

The number given after the name ofan

element is the _______ number.

4He

mass


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y In the previous examples, why is it ok to

omit the atomic number from our

representations?

Since the atomic number identifies

an element, you can check the

periodic table to find the atomic

number when given the symbol

because it never changes!


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Symbol At. # Mass # # p # n # e-

9 10

14 15

47 22

55 25

Complete the following table:

F 9 919

14Si 1429

2222Ti 25

25Mn 2530


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y Isotopes - ________________________

_________________________________________________________________

y

Since isotopes have the same number ofprotons, isotopes must be of the same

element.

y Remember that only protons and neutrons

contribute to the mass number, therefore,

isotopes must have different mass numbers.

Atoms containing the

same number of protons, but have adifferent mass number (# of n)


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y Despite these differences, isotopes are

chemicallyalike because theyhave

identical numbers of protons andelectrons. These subatomic particles are

responsible for the characteristic

chemical behavior of each element.

y To find the most abundant isotope using

atomic mass, round atomic mass to the

nearest whole number.

y Ex: atomic mass of oxygen is 15.9994,

most abundant isotope = O-16


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The three isotopes ofhydrogen are:The three isotopes ofhydrogen are:

y H 1 H 2 H 3

__p __n __p __n __p __n1 0 1 1 1 2


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Ions - ____________________________

________________________________

________________________________

atoms that lost or gained

electrons during a chemical reaction to

become electrically charged.

Symbol At. # Mass # # p # n # e-

24Mg 12

24Mg2+

35Cl

35Cl-

24 12 12 12

12 24 12 12 10

17 35 17 18 17

17 35 17 18 18


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Atomic MassAtomic Mass

y The mass of even the largest single atom is

too small to e measured on a balance. The

mass ofa single atom can be determinedusing __________________a mass spectrometer


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Mass SpectrometerMass Spectrometer


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y The mass ofan individualatoms is useful

information, but these values are inconvenient

and impractical to work with. Instead, it ismore useful to compare the relative masses of

atoms using an isotope of carbon, carbon 12,

as a basis. The isotope carbon 12 wasassigned a mass of exactly 12.00000 amu.

Therefore one amu is defined as:


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y Atomic mass unit (amu) - _____________

_________________________________

y An atom of carbon 12 has

__________________________; therefore,the mass ofa single proton or neutron is

about _______amu.

defined as 1/12

the mass of a carbon-12 atom.

6 protons and 6 neutrons

one


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y Since the mass ofa single atom depends

on the number of protons and neutrons

in the nucleus, one would think that the

atomic mass ofan element_____________________________should be a whole number


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y This is not the case due to the existence of

________.

y The atomic mass ofan element is the

____________________of the atoms in a

________________ sample of the

elements.

isotopes

weighted average mass

naturally occuring


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Calculating Atomic MassCalculating Atomic Mass

y To calculate the average atomic mass of

an element, one must know the number

of stable isotopes of that element, mass of

each isotope, and the natural percentabundance of each isotope.


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Example:

A sample of cesium is ,

19.7% 132Cs, and 5.49% 134Cs. What is itsaverage atomic mass?

Cs-132

Cs-134

(132 amu)

(134 amu)

(0.197)

(0.0549)

= 26.0 amu

= 7.36 amu

Add together 132.86 amu

132.9 amu


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y Electron Configurations_________________________________

__________________________

In all natural phenomena, change proceeds

towards the lowest possible energy state.

y Principal Energy Levels -___________

_________________________________

y The reference tables use a type of shorthand

which expresses the number of electrons in

each PEL.

placement of electrons around the

nucleus

(PELs) are

designated by the period number


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Looking at your Periodic TableLooking at your Periodic Table

2 e-

in 1st

PEL, 4 e-

in 2nd

PEL


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ExamplesExamples

y Neon _______________

y Magnesium ____________________

Ground State Electron Configurations

Lowest energy state ofan atom (most

stable.) These are given on the periodic

table.

2-8

2-8-2


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y Excited state electron configurations -

________________________________

________________________________________________________________

______.

When an electron in an atom gains a

specific amount of energy, that electronmoves to a higher energy state


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Example: HeliumExample: Helium

y Ground state He: 2

Excited state He: 1-1


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Example: NitrogenExample: Nitrogen

Ground State:2-5

Excited State:2-4-1


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Important note:Important note:

yThe number of electrons in

the ground state electron

configuration and theexcited state electron

configuration are the same!


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A sample regents question


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Acceptable answersAcceptable answers


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Try it yourself!Try it yourself!

y

What are some possible excited stateconfigurations forO?

y Ground state: 2-6


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Lewis Dot Diagrams orLewis Dot Diagrams or

Structures (Electron Dot)Structures (Electron Dot)

y Use only the ________ electrons.

y These are the electrons in the outermost

principle energylevel

valence

Therefore sodium

will have oneelectron in its

Lewis diagram


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y Represent electrons as dots (or circles or

Xs) around the element symbol.

y To draw a Lewis diagram foran atom,

follow the fill order:

two on top, then around the clock!


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y Therefore our example can be expressed

in two ways:

Na Na


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Other ExamplesOther Examples

M

g O

F


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BrightBright--Line SpectrumLine Spectrum

y

Every element emits light if it is heated bypassing electricity through its gas or vapor.

The atoms absorb energy, then lose the

energyand ___________.

y Please add: The energyabsorbed and emitted

is in discrete quantities. These quantities are

the difference in the principle energylevelsof the ground state configuration and the

excited state configuration

emit light


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The step are

analogous ofthe energy

levels, the ball

is analogous ofthe electrons!


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y Passing the light througha prism

(spectroscope) gives the ____________

__________(spectrallines) of the element.

This spectrum is unique for each element aseach element has a different number of

electrons, so ______

_______________________________________.

emissions

spectrum

no

two elements have the sameenergy


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Various Emissions SpectraVarious Emissions Spectra

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