chemical bonding

Question 1

define an ionic bond

Answer 1

an ionic bond is the strong electrostatic forces of attraction between oppositely charged ions.

Question 2

what does the actual structure of solid ionic compounds consist of?

Answer 2

the actual structure consists of continuously repeating three dimensional lattice with a uncountable large number of formula units of positive and negative ions.

Question 3

what is the structure formed by ionic compounds?

Answer 3

the giant ionic structure.

Question 4

what are the three characteristics of ionic compounds?

Answer 4

1. high melting point
2. conductor of electricity in molten and aqueous states
3. soluble in water but insoluble in organic solvent

Question 5

why do ionic compounds have a high melting point?
take note: they generally exist as solids at room temperature and pressure.

Answer 5

a large amount of energy is required to overcome the strong electrostatic forces of attraction between oppositely charged ions.

Question 6

why are ionic compounds conductors or electricity only in molten and aqueous states?

Answer 6

in the solid state, the oppositely charged ions are held in FIXED positions by strong electrostatic forces of attraction between oppositely charged ions. thus, ions are NOT FREE MOVING and cannot conduct electricity.

in the molten or aqueous state, the strong electrostatic forces of attraction between oppositely charged ions HAVE BEEN OVERCOME. the ions are free moving and can conduct electricity.

Question 7

what is needed to be present for a substance to be able to conduct electricity? (ionic compound)

Answer 7

free moving charged particles.

Question 8

what is a covalent bond?

Answer 8

a covalent bond is the sharing of electrons between non metal atoms.

Question 9

how is a non polar covalent bond formed?

Answer 9

it is formed when the two atoms in a covalent bond are the same / have the same electronegativity

Question 10

how it a polar covalent bond formed?

Answer 10

this bond is formed when the pair of shared electrons have different electronegativity values and are not equally shared between the two atoms.

Question 11

electronegativity increases across a _____ and decreases down a ____

Answer 11

electronegativity increases across a period and decreases down a group.

Question 12

what is electronegativity?

Answer 12

electronegativity refers to the ability of an atom to attract a share pair of electrons towards itself in a covalent bond.

Question 13

what are the three types of covalent substances?

Answer 13

1. simple molecule substances
2. giant molecular substances
3. macromolecules

Question 14

describe the structure of of simple molecular substances. (bond + force of attraction)

Answer 14

the atoms of each molecule are held together by strong covalent bonds while the molecules are held together by weak intermolecular forces of attraction.

Question 15

what are the properties of simple molecular substances?

Answer 15

1. low melting and boiling points
2. non conductor of electricity in any state
3. insoluble in water but soluble in organic solvent

Question 16

why do simple molecular structures have low melting and boiling points?

Answer 16

small amount of energy is required to overcome the weak intermolecular forces of attraction.

Question 17

why are simple molecular structures non conductors of electricity in any state?

Answer 17

there are no free moving electrons available to conduct electricity.

Question 18

describe the formation of giant molecular structures.

Answer 18

a giant molecular structure is formed when atoms form a network of covalent bonds throughout the structure.

Question 19

is a giant molecular structure many simple molecular structure bonded together?

Answer 19

NO. think of it as:
simple molecular structure = individual groups of atoms covalently bonded together with weak intermolecular forces
giant molecular structure = one whole group of atoms bonded together with strong covalent bonds between atoms.

Question 20

what are the properties of giant molecular structures?

Answer 20

1. high melting and boiling point
2. non conductor of electricity (there are exceptions: eg. graphite)

Question 21

what are allotropes?

Answer 21

allotropes are different forms of the same element. allotropes may have different properties such as hardness, electrical conductivity.

Question 22

what is one example of allotropes?

Answer 22

diamond and graphite.

Question 23

what structure is formed in any pure metal, and how is it formed?

Answer 23

a giant metallic lattice structure is formed. this structure is formed as metal atoms are closely packed together in the solid state.

Question 24

what happens to the valence electrons of metal ions when bonded together?

Answer 24

the valence electrons are DELOCALISED (they don’t belong to any metal atom anymore: valence electrons lost to become positive ions) and can move freely between the metal ions.
this results in a “sea” of free moving valence electrons.

Question 25

what is a metallic bond?

Answer 25

a metallic bond is the strong electrostatic forces of attraction between the positive metal ions and the “sea” of free moving valence electrons.

Question 26

what is the structure of alloys?

Answer 26

alloys are a type of solid-solid mixture of a metal with one or more other elements.

Question 27

why do alloys and metals have different properties?

Answer 27

in alloys, the regular arrangement of metal atoms is disrupted by the addition of other elements with atoms of different sizes, which are RANDOMLY DISTRIBUTED.

Question 28

what are the properties of metals?

Answer 28

1. metals have a high melting point
2. metals can conduct electricity in all states
3. metals are insoluble in water and organic solvents
4. metals are ductile and malleable

Question 29

what are the properties of alloys?

Answer 29

1. high melting point (but the melt over a range of temperatures)
2. can conduct electricity in all states
3. insoluble in water and organic solvents
4. ductile and malleable but harder and stronger than pure metals