Transcript Chemical Bonding

Notes 6 - Ions &
Chemical Bonding
Unstable Atoms
► In
order to be stable, an atom needs a
certain number of valence electrons
 2 valence e- if it only has 1 energy level
 8 valence e- if it has 2+ energy levels
► Most atoms are unstable
► In order to become stable, atoms may:
 take electrons from other atoms
 lose electrons to other atoms
 share electrons
► To
determine if an atom is stable or unstable,
you must look at the number of valence electrons.
Neon
Example: Neon has 8 electrons in the last level,
so it is stable
Carbon
► Carbon
Hydrogen
has 4 electrons in the last level, so it
is unstable
► Hydrogen has 1 electron in the last level, so
it is unstable as well
The Noble Gases
► Group
8 elements all
have 8 valence electrons
► They are naturally stable
► They do not give, take,
or share electrons
► They don’t react or form
bonds with other atoms
Ion Formation
► Ion
– an atom that gains or loses one or
more electrons
► Ions form so that atoms can become stable
► Atoms with a valence of 3 or less will lose
electrons
► Atoms with a valence of 5 to 7 will take
electrons
► When atoms lose or take electrons, they
become charged
Why do ions have a charge?
► Atoms
that have lost or gained electrons
have unequal numbers of protons and
electrons
► Atoms that gain electrons have more
electrons (e-) than protons (p+), so they
become negative ions
► Atoms that lose electrons have more
protons (p+) than electrons (e-), so they
become positive ions
Examples of Ions
Na+
Li+
Ca2+
Fe2+
Al3+
Cl-
F-
O2-
S2-
N3-
Metals vs Non-metals
► Metals
are unstable
► Metals have valences of 1,
2, or 3
► Metals give up valence
electrons and become
positive ions
► EX. Lithium
 Valence of 1
 Loses 1 electron
 Becomes a positive ion (Li+)
Metals vs Non-metals
► What
is a magnesium atom’s valence?
 2 (It is in Group 2 – that is how you know)
► So
how many electrons would it give up to
become stable?
2
► What
is a sodium atom’s valence?
1
► So
how many would it give up?
1
Metals vs Non-metals
► Non-metals
are unstable
except for the noble gases
► Non-metals have valences
of 4, 5, 6, or 7
► Non-metals take valence
electrons and become
negative ions
► EX. Chlorine
 Valence of 7
 Gains 1 electron
 Becomes a negative ion (Cl-)
Metals vs Non-metals
► What
is an oxygen atom’s valence?
6
► How
many electrons would it need to take
to become stable?
2
► What
is a fluorine atom’s valence?
7
► How
1
many would it need to take?
Chemical Bonding
► Chemical
bonding – when 2 or more
unstable atoms stick together in order to
become stable
► Chemical bond – an attractive force that
holds atoms together
► Atoms may bond together by:
 opposite ions attracting (positivenegative)
 sharing electrons
Chemical Bonding
►
There are 3 types of chemical bonds:
1. Ionic bonds
2. Covalent bonds
3. Metallic bonds
Ionic Bonds – What are they?
► Ionic
bond – a bond formed by the
attraction between positive and negative
ions
► Ionic bonds form between metal atoms and
non-metal atoms
 Metal atom forms the positive ion (gives e-)
 Non-metal atom forms the negative ion (takes
e-)
Ionic Bonds – How
do they form?
►A
non-metal atom with more
than 4 valence electrons takes
electrons from a metal atom
► The non-metal atom becomes a
negative ion
► The metal atom becomes a
positive ion
► The opposite ions attract
forming an ionic bond
► Ionic compounds are generally
solids with high melting points
(Ex. NaCl – Salt)
More Atom Humor
Covalent Bonds – What are
they?
► Covalent
bond – A bond formed when
atoms share one or more pairs of valence
electrons in order to become stable
 EX. H2O
► Atoms
that share more than one pair of
electrons may form double or triple bonds
 EX. O2
► Covalent
bonds form between atoms of
non-metals
Metallic Bonds – What are they?
► Metallic
Bonds – bond formed between
metal atoms
► Electrons can move between atoms
► Form between atoms of the same element
► 2 different metals can’t bond to each other
 Ex. Iron atoms can bond to iron atoms
metallically, but copper atoms can’t bond to iron
atoms
Remember…
► Unstable
atoms form bonds to become
stable
► Unstable atoms give, take, or share
electrons
► The Octet Rule – “I’ve got 8, so I’m
straight”
 Atoms with 8 valence electrons are stable