To bond or not to bond….
Chemical Bond: is a strong attractive force between atoms or ions in a compound.
Drawn as a stick or dots of electrons
Electrons bond
Valence electrons: electrons in the outer shell or orbital
Octet rule: most atoms prefer to have 8 electrons in their outer shells
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Chemical formula
Chemical formula: for a compound reveals the elements and their ratios in that compound
Atoms are chemically stable when their outer shells are full
NaCl CO
CaCl2 ZnO
CO2 Fe2 O3
FeO
Ions
Ionic bond: a force of attraction between two oppositely charged ions
Ions: are charged particles that form when atoms gain or lose electrons
These atoms are said to have charges
Calculate charges
by subtracting the number electrons of from the number of protons
Anion
Atoms that gain electrons form negative ions
Anion: Negatively charged ion
Cation
Atoms that lose electrons form positive ions
Cation: positively charged ion
Cats are positively cwazy
Ions
Charged ions that bond form a neutral compound as in salt Na+ Cl-
Energy is required and can either be given off or absorbed when electrons move
In ionic compounds the ions will often disassociate in water
Ions are important in your nerve and muscle cells – often called electrolytes
Covalent bonds
Covalent bonds: Atoms share electrons
Molecules are formed from at least two covalently bonded atoms
Water has a covalent bond
:
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Covalent Bond
Between nonmetallic elements of similar electronegativity.
Stable non-ionizing particles, they are not conductors at any state
Examples; O2, CO2, C2H6, H2O, SiC
Bonds in all the polyatomic ions and diatomics
are all covalent bonds
Electonegativity
Electronegativity: the pull one atom has for another atom's electrons during the bonding process.
Electronegativity determines what type of bond will be formed
when electrons are shared equally
NONPOLAR COVALENT BONDS
Diatomic again
Diatomic molecules are two atoms bonded together
O, H, N, and all halogens often called diatomic elements
2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom
Oxygen Molecule (OOxygen Molecule (O22))
Polar express
Polar Molecule has a positive end and a negative end
This is caused by uneven sharing of electrons
Nonpolar molecules do not have positive or negative ends- they share evenly
- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
Polar vs. Nonpolar
Oxidation numbers
Oxidation number: shows the combining ability of an element in a compound
Na +1 Mg +2 Cl –1 B +3
Some elements have more then one oxidation state
Fe, Cu, Cr, Pb, Sn We must indicate
the oxidation state when writing these compounds or elements
Fe (III), Cu (II), Sn (II),
.
Bond type is determined by electonegativity
Naming Covalent Compounds
Covalent compounds are named by adding prefixes to the element names.
The compounds named in this way are binary covalent compounds.
‘Binary’ means that only two atom are present.
‘Covalent’ (in this context) means both elements are nonmetals.
A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.)
A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘ide’.
Naming Covalent Compounds
Prefixes
Subscript Prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
Subscript Prefix
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.
Naming Binary Covalent Compounds: Examples
N2S4 dinitrogen tetrasulfide
NI3 nitrogen triiodide
XeF6 xenon hexafluoride
CCl4 carbon tetrachloride
P2O5 diphosphorus pentoxide
SO3 sulfur trioxide
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
7 heptaa
8 octa
9 nona
10 deca
* Second element in ‘ide’ from
* Drop –a & -o before ‘oxide’
Writing formulas
1.Symbol with a positive oxidation number is first (metals always have positive oxidation numbers)
2.Symbol with negative oxidation number
3.Write subscripts so oxidation number of the compound totals zero
Use parantheses around polyatomic ions if using multiples of these
Polyatomic
A group of covalently bonded atoms which have charge.
Usually negatively charged Treat polyatomic ions as if they are
one thing, don’t mess with their subscripts.
Naming
Write the name of the positive ion Write the root of the negative ion-
( ox, flor, chlor, iod,etc.) and add ide. For polyatomics just write the name
of the ion For multivalent metals tell valence
state using roman numerals in paranthesis. Ex. Iron (II) chloride
Practice
Formulas Naming
Calcium hydroxide Ca(OH)2
Aluminum bromide AlBr3
Iron (III) sulfate Fe2(SO4)3
Silver nitrite AgNO3
CuO Copper (II) oxide LiNO3
Lithium nitrate (NH3)2CrO4
Ammonium chromate Sr(C2H3O2)2
Strontium acetate