Chapter 2, Section 1 Inside an Atom
I.
Structure of an atom
 Nucleus surrounded by one or more electrons
 Nucleus has protons and neutrons
 Protons have a positive charge, neutrons have
no charge
 Electrons move in all directions, have a
negative charge
 Protons & neutrons are same size, 2,000
times as big as electrons
II. Electrons in atoms
 Move too fast to know exactly where it is at
any one time
 Little particles, big spaces
 Atom’s volume is the space the electrons
occupy.
 Is huge compared to nucleus
 Valence electrons
 Electrons move in specific layers
 Layer furthest away are the valence
electrons.
 They are the only electrons involved in
chemical bonding
 Electron dot diagram shows the valence
electrons
III.
Why atoms form bonds
 Neutral atom never has more than 8 valence
electrons. Atoms with either 8 or 0 valence
electrons are less reactive (or more stable)
than they were before
 A chemical bond forms when valence
electrons move between 2 atoms. They may
be transferred or shared
Chapter 2, Section 2 Atoms in the Periodic
Table
IV. Organizing the elements
 Organization is based on how elements react
 Atomic number is number of protons in
nucleus
 Table organizes so number of protons
increases left to right, top to bottom
 Columns are called groups of families
 Rows are called periods
 Valence electrons increase across a period
V. Comparing families of elements
 Noble gases
 Group 18 elements all have 8 valence
electrons (except helium)
 They are inert, meaning inactive, so do not
react easily
 Reactive nonmetals
 Group 17 (called Halogen family) elements
are very reactive. They are close to a full
valence shell, so they readily grab any
available electron
 Reactive metals
 Group 1 (called alkali metals) also very
reactive. With 1 valence electron, they
donate it freely
Chapter 2, Section 3 Ionic Bonds
VI. Electron Transfer
 An ion is an atom that has become
electrically charged, by gaining or giving up an
electron.
VII.
Forming an ionic bond
 Positive and negative charges attract each
other, so positive and negative ions will form a
bond.
 Salt is an example. Sodium (Na) gives up an
electron, so is a positive ion. Chlorine (Cl)
takes the electron, so it is a negative ion.
The opposites then bond to each other
VIII. Polyatomic ions
 A compound can be an ion. The carbonate ion
is CO32-. It is commonly found in calcium
carbonate, which is found in Tums and other
antacids
IX. Naming ionic compounds
 Positive ion is first, and is usually the name of
the elements
 Negative ion adds –ide to name of element.
X. Properties of ionic compounds
 Crystal shape
 Ions form orderly arrangements, which are
crystals. Positive ions want to be as far
away as possible from other positives and
as close as possible to negatives.
 High melting points
 All ionic compounds are solid at room
temperature
 Multiple bonds in crystal structure are hard
to break, so do not melt easily
 Electrical conductivity
 When dissolved in water (or melted), ionic
compounds freely conduct electricity.
Electrons are free to move.
 Not true in a solid, where electrons are
tightly held in place.
Chapter 2, Section 4 Covalent Bonds
XI. Electron sharing
 Instead of taking/getting an electron, atoms
may share an electron or two.
 The shared electron forms a covalent bond
XII.
How many bonds?
 Will form bonds to bring number of valence
electrons up to 8
 Example, oxygen has 6 valence electrons, so it
forms 2 bonds with hydrogen, to bring total
to 8
 Sometimes get double bonds, where the
atoms share 2 or 3 pairs of electrons
XIII. Properties of molecular bonds
 Covalent bonds form molecular compounds
 Melting and boiling points are much lower than
ionic compounds. Bonds between the atoms
are stronger, but bonds between molecules
are weaker.
 Poor conductors of electricity
 Water does not conduct electricity, so why
worry about hair dryer in bathtub?
XIV.
Unequal sharing of electrons
 If one pulls much more strongly, electron
spends more time there, giving a slight
negative charge to that side of the bond or
molecule. That is called “polar”
 Difference between polar bonds and polar
molecules. May have polar bonds lined up to
cancel each other out, and get a nonpolar
molecule
 Nonpolar molecules
 Atoms pull equally strongly on electrons so
they stay balanced, with no charges, or
polar bonds cancel out
 Polar molecules
 Water is polar because the polar bonds do
not cancel each other out
XV. Attractions between molecules
 Water molecules are attracted to each
other, positive pole to negative pole
 That is why water has surface tension
 Carbon dioxide molecules are not, because
they are nonpolar
 Oil and water don’t mix because one is polar
and the other nonpolar. Soap has a polar end
and a nonpolar end