Lecture IAtomic Structure Review

Distinguishing Between Atoms

I. Atomic Structure Review Rutherford Model of the Atom

Three subatomic particles

Nucleus: Center of atom-contains

Protons:

(+) charge

1 atomic mass unit

Neutrons:

no charge

1 atomic mass unit

Orbitals:

Paths around nucleus-great distance from nucleus-contain

Electrons:

(-)charge

1/1840 amu

II. Atomic Number Atomic Number: The

number of protons in the nucleus.

Elements differ because of different number of protons

Because atoms are neutral, (+) charge = (- )charge / protons = electrons

ElementElement Atomic Atomic

NumberNumber

ProtonsProtons Elec-Elec-

tronstrons

KK 1919 ________ 1919

________ ________ ________ 55

SS 1616 ________ ________

VV ________ 23 23 ________

III. Mass Number Mass Number: The total number of

protons and neutrons in an atom. Most mass is concentrated in nucleus-that is where

these particles are located If you know the atomic number and mass number

you can determine atom’s composition. # neutrons = mass # - atomic number Shorthand Notation / Nuclear Notation

Symbol with mass as superscript 197Auatomic number as subscript 79

Element Hydrogen

oxygen

# protons

# electrons

# Neutrons

Mass Number

Atomic Number

Nuclear Notation 1H

1

197Au79

35Cl17

38Cl17

Element Hydrogen

oxygen Gold Chlorine

Chlorine

# protons

1 8 79 17 17

# electrons

1 8 79 17 17

# Neutrons

0 8 118 18 21

Mass Number

1 16 197 35 38

Atomic Number

1 8 79 17 17

Nuclear Notation 1H

1

16

8 O

197Au79

35Cl17

38Cl17

IV. IsotopesA. Isotopes: atoms that have the same

number of protons and electrons but different number of neutrons.

Different masses mean they have different mass numbers

Chemical behavior is the same Three isotopes of hydrogen: hydrogen,

deuterium, tritium

Isotope Nuclear Notation

Protons Electrons

Neutrons

Mass Number

Protium 1H

1

Deuterium

2H1

Tritium 3H

1

V. Atomic MassA. Because mass of atoms so small and

inconvenient to work with (fluorine 3.155 X 10-23) it is more useful to compare relative masses of atoms using a reference isotope as a standard. Carbon-12 is used.

B. Atomic Mass Unit (amu) = 1/12 mass of carbon atom.

C. Atomic mass: weighted average mass of naturally occuring isotopes.

D. Estimate atomic mass: look at relative abundanceE. Calculate atomic mass: multiply the mass of each

isotope by its natural percent abundance (expressed as a decimal) also known as the relative abundance, and add products.

Calculate Atomic Mass of Sulfur

Nuclear Notation

Natural Percent Abundance

Mass (amu)

Relative Abundance

32S16

95.002 31.972

33S16

0.76 32.971

34S16

4.22 33.967

36S16

0.014 35.967

Calculate atomic mass: multiply the mass of each isotope by its relative abundance and add products.

VI. The Periodic Table-A PreviewThe periodic table allows you to easily

compare one element to another.

Horizontal rows are called periods.

Vertical columns are called groups or families.

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