·
Noble gases don’t react because they have 8
valence electrons.
·
Compounds are the result of the formation of
chemical bonds between two or more different elements. Ionic bonds occur when
atoms of one element lose valence electrons and atoms of another element gain
electrons. These bonds typically happen between metals and nonmetals.
·
In the formation of either an ionic bond or
covalent bond, atoms lose, gain, or share, valence electrons to acquire an
octet.
·
An atom is happiest with 8 valence electrons
·
Metals react with nonmetals
·
In ionic bonding, valence electrons of metals
transfer to nonmetals because their ionization energies are low (groups 1A, 2A,
and 3A). When they do this, they acquire the arrangement of noble gases
(usually 8 valence electrons) and form IONS with positive charges.
·
Metals in ionic compounds lose their valence
electrons to form positively charged ions called cations.
·
Nonmetals form negative ions when they gain
valence electrons to attain an octet. Ions with negative charges are called
anions.
·
If an atom loses an electron, the number of
protons is greater and it becomes ionic. The new difference between protons and
neutrons is the ionic charge.
·
The name of an anion uses –ide to replace the
last syllable of the element name
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Example: F + Li
o
F has 9P and 10N in the nucleus, one layer with
2 electrons and an outer layer of 7 electrons
o
Li has 3P and 4N in the nucleus, one layer with
2 electrons and an outer layer of 1 electron
o
The one electron from Li goes over to F because
it’s easier to move 1 than 7
o
The Li becomes a cation and the F becomes an
anion
o
This would be an ionic bond because they are
both stable
·
In ionic compounds, the attraction is very
strong so the melting points are extremely high. At room temp, ionic compounds
are solids.
·
The formula of an ionic compound indicates the
number and kinds of ions that make it up. The sum of ionic charges in the
formula is always zero.
·
Subscripts in the formula of an ionic compound
represent the number of positive and negative ions that give an overall charge
of zero. It means that ___ was needed to make a charge of zero. So if you have
one element that has a greater charge than the other, you have to ass however
many of the other element so make them equal out.
·
In the formula of an ionic compound, the cation
is written first followed by the anion.
·
All polyatomic ions are negative except for
ammonium.
·
Transition metals usually form two or more kinds
of positive ions because they lose their outer electrons as well as electrons
from a lower energy level. It is not possible to predict the ionic charge from
the group number. They have a “variable valence”. A Roman numeral is used to match
the ionic charge. Some metals that form more than one positive ion are:
o
Chromium (2 and 3), Copper (1 and 2), Gold (1
and 3), Iron (2 and 3), Lead (2 and 4), and Tin (2 and 4)
·
An ionic compound with 3 or more elements
contains some type of polyatomic ion, which is a group of atoms that has an
ionic charge. There is only one positively charge polyatomic ion: NH4+
·
No polyatomic ion exists by itself, it must be
associated with ions of opposite charge, the bond is electrical.
·
When more than one polyatomic ion is needed for
charge balance, parentheses are used to enclose the formula of the ion and a
subscript is written.
·
Ionic compounds having two elements are named by
naming the first element, followed by the second element, with an –ide ending.
If more than one positive ion is possible, write a Roman numeral for the ionic
charge following the name of the metal.
·
Covalent compounds are created because atoms of
nonmetals have high ionization energies and do not lose electrons easily. The
atoms are shared to achieve stability and molecules are formed. This satisfies
the octet rule.
·
In Period 2, the number of electrons that an
atom shares and the number of covalent bonds it forms are usually equal to the
number of electrons needed to acquire a noble gas arrangement (satisfy the
octet rule).
·
There are elements that exist as diatomic
molecules (there has to be two of them): H, N, O, F, Cl, Br, I
·
If the first name is a metal than it’s ionic,
otherwise it’s covalent.
·
Electronegativity is the attraction of an atom for
valence electrons in a chemical bond. Nonmetals have higher electronegativity
values because they have a greater attraction for electrons than nonmetals.
Fluorine has the highest level. The values increase from left to right across
each period and from bottom to top of each group.
·
Ionic bonding means electrons are transferred,
covalent bonding means that electrons are shared.
·
A covalent bond between atoms with identical or
very similar electronegativity values is a nonpolar
covalent bond.
·
When electrons are shared unequally, the bond is
a polar covalent bond. The shared electrons are attracted to the more
electronegative atom, which makes it partially negative, while the atom with
the lower electronegativity becomes partially positive. It has a separation of
charges called a dipole.
·
When electronegativity differences are from 0.0
to 0.4, the electrons are shared about equally in a nonpolar covalent bond.
·
When the differences is greater than 0.4 but
less than 1.8, the bond is a polar covalent.
·
Differences greater than 1.8 are ionic.
·
VSEPR (valence shell electron pair repulsion)
theory indicates that electron groups will move as far apart as possible to
reduce the repulsion between their negative charges.
·
A molecule with two or more polar bonds can be a
nonpolar molecule if the polar bonds have a symmetrical arrangement in the
molecule.
·
In a polar molecule, one end of the molecule is
more negatively charged than another end. Polarity occurs when the polar bonds
do not cancel each other out.
·
When a hydrogen atom is attached to highly
electronegative atoms of fluorine, oxygen, or nitrogen, there are strong
dipole-dipole attractions between the polar molecules. This type of attraction
is called a hydrogen bond.
·
When writing compounds, the metal takes the number
that is on top of the other element: Li+ and CO32-
= Li2CO3
o
Another example: Cu2+ and OH-
= Cu(OH)2
o
****don’t forget that polyatomics just get
parentheses around them*****
·
Just remember:
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To check and see if any of the compounds are
polyatomic ions
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Look at the ionic charge on your metal because
that will become a subscript on your second part of the compound if the second
part doesn’t have an exponent
o
If the second part does have an exponent, than
it becomes a subscript on the metal (first part of compound) even if it’s a
polyatomic
o
If it’s one of the transition metals with a
Roman numeral, the Roman numeral becomes a subscript of the second part of the
compound.
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