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),

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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