Chemical Composition - Bonding

Question 1

element

Answer 1

is a substance that cannot be split up into simpler substances by chemical means, it is made of one type of atom that all have the same atomic number

Question 2

compound

Answer 2

a substance that is made up of two or more different elements combined together chemically

Question 3

octet rule

Answer 3

states that atoms on reaction tend to reach an electron arrangement with eight electrons in the outermost energy level

Question 4

limitations of the octet rule

Answer 4

• hydrogen + lithium: react to form helium and have 2 electrons in the outermost energy level
• atoms in the d block: don’t obey the octet rule
• sulfur + phosphorus: don’t always follow the octet rule
• beryllium + boron: do not obey the octet rule because they can’t reach 8 electrons in the outermost energy level

Question 5

valency

Answer 5

the number of electrons that an atom needs to gain, share or lose in order to attain a stable electron configuration

Question 6

valence electrons

Answer 6

the electrons in the highest occupied energy level of an atom. the number of valence electrons determines the valency of the atom and chemical properties of the atom

Question 7

ion

Answer 7

an atom/group of atoms that has either lost or gained electrons and has become positively (cation) or negatively (anion) charged

Question 8

ionic bond

Answer 8

the electrical attraction between oppositely charged ions which are produced when electrons are transferred from one atom or another

Question 9

properties of ionic compounds

Answer 9

the strong ionic bond between the ions in the lattice requires a lot of energy to break up the lattice:
- exist as large crystalline solids (lattice)
- have high melting points
- have high boiling points
- are hard solids
- do not conduct electricity in the solid state - ions are held tightly and not free to move
- conduct electricity when molten or in solution - ions are free to move
- dissolve in water to some extent
- water molecules are polar and attracted to the ions in the lattice

Question 10

covalent bonding

Answer 10

when two or more atoms share electrons to fill their outer shell

Question 11

properties of covalent substances

Answer 11

• most are liquids/ gases at room temperature
• some are solids with low melting and boiling points
• do not conduct electricity when in liquid or in solution
• do not dissolve in water