foundations in chemistry

Question 1

how many electrons can the 1st-4th shells hold

Answer 1

1 - 2 electrons
2 - 8 electrons
3 - 18 electrons
4 - 32 electrons

Question 2

electrons are located in shells at different energy levels, what kind of energy levels are shells closest to the nucleus at

Answer 2

the lowest energy level

Question 3

what is an orbital

Answer 3

region of space that can hold up to 2 electrons

Question 4

what determines which block of the periodic table an element is found in

Answer 4

which highest energy orbital is filled.

eg. if highest energy electron is found in a d-orbital, then element will be in d-block

Question 5

what is an equation to work out the number of electrons in a shell

Answer 5

2 x n (the shell number) ^ 2

Question 6

what is the bond angle of a molecule with a tetrahedral shape, what gives it it’s shape

Answer 6

109.5

4 bonding regions, no lone pairs, bonding pairs repel equally

Question 7

what is the bond angle of a molecule with a pyramidal shape,
why does it have this shape

Answer 7

107

3 bonding regions, one lone pair, lone pair repel more strongly than bonding pairs

Question 8

what is the bond angle of a molecule with a non linear shape, why does it have this shape

Answer 8

104.5

2 bonding regions, 2 lone pairs
lone pairs repel more strongly than bonding pairs

Question 9

what is the bond angle of a molecule with a linear shape, why does it have this shape

Answer 9

180

1 bonding region
(sometimes 3 lone pairs)
lone pairs repel more strongly than bonding pairs

Question 10

what is the bond angle of a molecule with a trigonal planar shape, why has it got this shape

Answer 10

120

3 bonding regions, no lone pairs, all bonding pairs repel equally

Question 11

what is the bond angle of a molecule with an octahedral shape, why does it have this shape

Answer 11

90

6 bonding regions, no lone pairs, all bonding pairs repel equally.

Question 12

what is the bond angle of a molecule with a square planar shape

Answer 12

90

Question 13

what is electronegativity

Answer 13

the ability of an atom to attract the bonding electrons of a covelant bond towards it.

Question 14

what can two atoms of differing electronegativity in a covelant bond end up as

Answer 14

a permanant dipole

(this is only if the dipoles are not symmetrically arranged, and so do not cancel each other out)

Question 15

how can u test if a molecule is polar or non polar

Answer 15

polar molecules dissolve in polar solutions.

non polar molecules will not dissolve in polar solutions.

Question 16

what would give a higher metling point, temporary dipole bonding or permanent dipole bonding

Answer 16

permenant dipole bonding

Question 17

when does hydrogen bonding occur

Answer 17

if a H atom is directly attached to N, O or F

Question 18

what are the two anomalous properties of water caused by hydrogen bonding

Answer 18

ice is less dense than water

higher boiling point and freezing point than would be expected

Question 19

why is ice less dense than water

Answer 19

the strong hydrogen bonds in ice cause an open lattice to form in the solid state

Question 20

why does water have a higher boiling point than expected

Answer 20

strong hydrogen bonds that require lots of energy to overcome

Question 21

what are 2 factors that affect the strength of intermolecular forces

Answer 21

• number of electrons, high number of electrons, larger uneven distribution of electrons, stronger london forces.
• is molecule contains atoms of very different electronegativity, larger dipole meaning stronger permanent dipole-dipole interactions.

Question 22

what are the rules for assigning oxidation numbers

Answer 22

1. group 1 metals
2. group 2 metals
3. fluorine
4. hydrogen
5. oxygen
6. chlorine

Question 23

what is mean by atomic number

Answer 23

the number of protons in one atom of an element

Question 24

what is meant by mass number

Answer 24

the number of particles present in the nucleus of one atom of an element (protons + neutrons)

Question 25

what is meant by relative atomic mass

Answer 25

the weighted average mass of one atom of an element relative to 1/12th the mass of one atom of C12

Question 26

define relative isotopic mass

Answer 26

the mass of one atom of an isotope relative to 1/12th the mass of one atom of carbon 12

Question 27

what is meant by the term weighted average mass

Answer 27

the average mass taking into account the relative abundance of isotopes

Question 28

what is the formula linking mass, volume and density

Answer 28

mass = volume x density

Question 29

what is the difference between Ar and Mr

Answer 29

Ar - atomic mass of one atom of an element

Mr - average mass of a molecule, worked by adding all the Ar together.

Question 30

what is meant by an isotope

Answer 30

atoms of the same element, with same number of protons, different number of neutrons.

Question 31

when is relative formula mass used instead of relative molecular mass

Answer 31

when dealing with ionic compounds

Question 32

define empiricle formula and molecular formula

Answer 32

empiricle formula - the simplest whole number ratio of each element in the compound

molecular formula - the actual number of atoms of each element in a molecule of a compound.

Question 33

what is meant by avagadro’s constant

Answer 33

the amount of substance that contains as many particles as exactly 12 g of C12. number of particles is 6.02 x 10 ^ 23

Question 34

if in a question see (RTP), what can we tell

Answer 34

one mole of molecules of any gas at room temperature pressure takes up 24 dm ^3

can use N = v/24

Question 35

why is percentage yield not always 100

Answer 35

not all reactants react
side reactions occur
some is lost in the process of making.

Question 36

why are isotopic masses and relative masses compared to C12

Answer 36

The mass of a C12 atom acts as the. standard for atomic masses.

Question 37

how do u convert from mol dm ^-3 to g dm ^-3

Answer 37

multiply by Mr

Question 37

what are the benefits for sustainability of developing chemical processes with a high atom economy

Answer 37

high % economy is less expensive, as less money and time is spent on separating the desired product from waste products.

high % economy means less waste products are produced

reactions are more sustainable because they use raw materials which are renewable and will never run out.

Question 38

why do isotopoes have the same chemical properties

Answer 38

they have the same number of electrons in outer shell

DO NOT say ‘ same number of electrons ‘