Properties of Atoms and the
Periodic Table
Chapter 18
18-1: Structure of the Atom
Atoms


Atom – the smallest unit of matter that can’t
be broken down by chemical means
Atoms are made up of three types of
particles:



Proton: (+) charged
Neutron: no charge
Electron: (-) charged
Nucleus – consists of
protons and neutrons
Atoms


A proton is about 1000 times larger than an
electron
Electron cloud – the region where electrons
orbit the nucleus
18-2: Masses of Atoms
Atomic Mass

Atomic mass =


protons + neutrons
Atomic number - The
number of protons in
the nucleus of an atom,
which determines its
place in the periodic
table
Atomic Mass

Atomic Facts

Atomic number = protons = electrons

Atomic mass
- Atomic number
# of neutrons

Maximum number of electrons



1st energy level – 2 electrons
2nd energy level – 8 electrons
3rd energy level – 18 electrons
Atomic Mass

Element – A substance
made up a group of
similar atoms that have
the same number of
protons
Atomic Mass

Isotopes – Atoms of an
element that have
different numbers of
neutrons
Chemical Bonds

Valence electron – An electron that is found
in the outermost shell of an atom

Lewis dot diagrams can be used to show the
transfer of valence electrons
Chemical Bonds

Chemical bonds form between groups of
atoms because most atoms become stable
when they have eight electrons in the valence
shell (Octet rule)
Chemical Bonds

Compound – A substance made of the
bonded atoms of two or more different
elements
Chemical Bonds

Ion – an atom or group of atoms that has an
electric charge because it has gained or lost
electrons

Ionic bond – the attractive force between
oppositely charged ions
Chemical Bonds


Covalent bond – chemical bond that shares
electrons
Molecule – A group of atoms held together by
covalent bonds
Chemical Bonds

Hydrogen bond - A chemical bond in which a
hydrogen atom of one molecule is attracted
to an electronegative atom
Chemical Bonds
Polarity


Polar – molecules with
partial charges on
opposite ends
Water is the most
abundant compound in
organisms
Average Atomic Mass

Average atomic mass is not a straight
average but a weighted average based upon
the percent isotopic ratio of the element.

(Mass1 x % Isotope1) + (Mass2 x % Isotope2) + (etc.)
100
100
Average Atomic Mass

43.00% of 74.2 amu; 57.00% of 77.1 amu

(Mass1 x % Isotope1) + (Mass2 x % Isotope2) + (etc.)
100
100
(74.2 amu x 43.00) + (77.1 amu x 57.00)
100
100
(3190.6 amu) + (4394.7 amu)
100
100
31.906 amu + 43.947 amu
75.853 amu




18-3: The Periodic Table
The Periodic Law

The modern periodic table is based on
atomic number, or number of protons.
The Periodic Law

Period – Each row in the table of elements


Hydrogen, the first element in Period 1, has one
electron in its first energy level.
Lithium, the first element in Period 2, has one
electron in its second energy level.
The Periodic Law

Group – Each column in the periodic table

The elements in a group have similar electron
configurations
The Periodic Law
Classes of Elements

Metals – elements that are good conductors
of electric current and heat

Except for mercury, metals are solids at room
temperature
Classes of Elements

Metals (cont.)


Malleable – able to be hammered or pressed
permanently out of shape without breaking or
cracking
Ductile – can be drawn into thin wires
Classes of Elements

Transition metals – elements that form a
bridge between the elements on the left and
right sides of the table

Many of their compounds are colored
Classes of Elements

Nonmetals – elements that are poor
conductors of heat and electric current



Many nonmetals are gases at room temperature
Nonmetals that are solids at room temperature
tend to be brittle
Brittle – hard but liable to break or shatter easily
Classes of Elements

Metalloids – elements with properties that fall
between those of metals and nonmetals
18-3: Representative Groups
Representative Groups

Elements in a group have similar
properties because they have the same
number of valence electrons
Representative Groups

Alkali metals – (Group 1A) These metals
have a single valence electron and are
extremely reactive
Representative Groups

Alkaline earth metals (Group 2A) – have
two valence electrons
Representative Groups

Boron family (Group 3A) – have three valence
electrons
Representative Groups

Carbon family (Group 4A) – have four
valence electrons

Clay used to
produce this
pottery contains
silicon
Representative Groups

Nitrogen family (Group 5A) – have five valence
electrons

The numbers on the bags of fertilizer are,
from left to right, the relative amounts of
nitrogen, phosphorus, and potassium.
Representative Groups

Oxygen family
(Chalcogen) –
(Group 6A) have six
valence electrons
Representative Groups

Halogens (Group 7A) – have seven
valence electrons
Representative Groups


Noble gases (Group 8A) – Helium has two
valence electrons. Each of the other noble gases
has eight valence electrons.
Noble gases are extremely
unreactive