Atomic Structure

Topic 1

Objectives:• To understand how the model of the atom

has changed • To know the subatomic particles and all

their properties• To understand electrons and their

energies• To be able to distinguish between ground,

excited state and ion configurations• To distinguish between different types of

matter

Early Studies of Matter

• The model of the atom is the work of many scientists over a long period of time

• Greeks– Fire, air, water, and earth

• Boyle – 1600s– Gold and silver are elemental

Dalton – 1700s• Atom = basic unit of matter• cannonball• Dalton’s Atomic Theory

• All elements are composed of indivisible atoms• All atoms of a given element are identical• Atoms of different elements are different; (different

masses)• Compounds are formed by the combination of

atoms of different elements

• Not all correct today but the groundwork

Thomson – “Plum Pudding”

• Electron

• Atom has some negative charged particle found within

Rutherford’s Gold Foil Experiment

• Nucleus of atom discovered• Nuclear model• Experiment:

– Alpha particle shot at a piece of gold foil

Results Conclusion

Most particle went through

Some were deflected

Rutherford’s Gold Foil Experiment

Bohr Model

• Planetary model

• Electrons in definite fixed orbits

• How we draw them

Wave-Mechanical Model

• Most modern model of the atom

• Gives electrons properties of both particle and wave

• Electrons with distinct amounts of energy moving in orbitals

• Orbitals = region in which electron is likely to be located

Structure of the Atom

• Positive nucleus and negative electrons in regions called orbitals outside nucleus

Proton Neutron Electron

Charge

Mass

Location

Atomic Number

• Atomic Number is the number of protons

Atomic number = # protons

• Each element has its own atomic number…it identifies what element you have

Complete Chart

Atomic Number 4

# protons 32 80Element symbol Xe

Atom is neutral• Neutral means equal amount of positive

and equal amount of negative

• SOOO…. WHAT 2 SUBATOMIC PARTICLES WILL BE EQUAL IN AN ATOM?

• Remember: APE

Mass Number

• Mass number is the mass of the nucleus (protons + neutrons)

Mass # = #protons + #neutrons

Mass # - #protons = #neutrons

• Notation: C-12 12

6C

Complete Chart

Element symbol

Atomic number

Mass number

# protons

# neutron

C 812 6

17 18

Isotopes

• Isotopes are atoms of the same element that have different numbers of neutrons (giving them different mass numbers)

• Same: #protons (atomic numbers)

• Different: #neutrons (mass numbers)

Atomic Masses

• Average masses of all the naturally occurring isotopes

• Weighted average

Finding Atomic Mass Problems

• Carbon has 2 naturally occurring isotopes. 98.89% of C’s are C-12 with a mass of 12 amu. The remaining 1.108% are C-13 with a mass of 13 amu. What is the atomic mass of carbon?

Isotope Mass Abundance

(decimal or percent key)

Total

for isotope

TOTAL

Atomic Mass

Sample Problem

Element X three isotopes; one that occurs 72.0% with a mass of 84.9 amu, the second that occurs 18.0% with a mass of 87.0 amu, and the last that occurs 10% with a mass of 89.1 amu. Find the average atomic mass of Element X.

SolutionIsotope Mass Abundance Total for

isotope

Electrons, Electrons, Electrons

• Electrons surround the nucleus in regions called orbitals

• Electron Configurations for the atom are on the reference tables– Tells how many electrons are in each energy

level– Last number in electron configuration is

number of valence electrons (outermost electrons)

Sample Questions

• Write the electron configuration of the following atoms:– Sodium– Chlorine– Fe

• Circle the valence electrons in the above atoms

Energy of Electrons

• Each electron has its own distinct amount of energy that corresponds to the energy level that it occupies

– Higher the energy level the higher the electron’s energy

Ground vs. Excited State• Electrons can gain or lose energy making

them move to higher or lower energy levels

• Ground State: electrons in their normal energy levels; stable– Found on the reference table

• Excited State: electron gains energy and moves up to a higher energy level– Start with configuration on table, keep same

number electrons, but change the order

Continued

• Ground Excited; energy is __________

• Excited Ground; energy is __________

• Calcium atom’s electron configuration is…– Ground state:

– Excited state:

Sample Problems

Atom Ground State

Excited State

Cl

K

O

Sample Problems

• Which shows an increase in energy?A - Electron that goes from the 2nd shell to the

3rd shell

B - Electron that goes from the 3rd shell to the 2nd shell

• Which of the above A or B will produce a light spectrum?

Ionic Radii

Types of Matter

• Matter – anything that has mass and takes up space (volume)

• Homogeneous – uniform composition– Can contain more than one type of particle,

but the particles have to be evenly mixed– Sugar water

• Heterogeneous – varying composition– Parts have there own chem and phys

properties– Chocolate chip cookie

Matter

Pure Substance

Mixtures

Compound Element SolutionsAll other heter. mixs

Definitions

• Pure Substances – composition is the same throughout

– Element – substances that cannot be broken down or decomposed into simpler substances by chemical means

– Compounds – two or more elements that are chemically combined in definite proportions by mass

• Law of definite proportions – types of atoms in a compound exist in a fixed ratio

– H2O2 vs. H2O

– H2O: mass ratio of 1:8

• Mixtures – combinations of two or more pure substances that can be separated by physical means (not in “fixed” ratios)

– Heterogeneous mixtures

– Homogenous mixtures = solutions