Atomic structure

Question 1

relative mass of electron

Answer 1

1/1836

Question 2

why do isotopes have same chemical characteristics

Answer 2

because they have the same number of electrons in their outer shells

Question 3

what is ionisation energy

Answer 3

amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions

Question 4

second ionisation energy

Answer 4

energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 5

formula for third ionisation energy

Answer 5

X2+ (g) → X3+ (g) + e-

Question 6

why does successive ionisation energy of an element increase

Answer 6

because once you have removed the outer electron from an atom, you have formed a positive ion

Removing an electron from a positive ion is more difficult than from a neutral atom

As more electrons are removed, the attractive forces increase due to decreasing shielding and an increase in the proton to electron ratio

Question 7

when do lobes of p orbitals become larger and longer

Answer 7

with increasing shell number

Question 8

what is periodicity

Answer 8

elements across the periods show repeating patterns in chemical and physical properties

Question 9

difference between plum pudding and nuclear model

Answer 9

In the plum pudding model, atoms were described as being made from electrons embedded within a positive sphere,

whereas in the nuclear model the nucleus is a positive structure at the centre of the atom, with negative (and much smaller) electrons ‘orbiting’ around the outside of it

Question 10

definition of relative atomic mass and relative isotopic mass

Answer 10

relative atomic mass: mean mass of an atom of an element relative to 1/12 of the mean mass of an atom of the carbon 12 isotope

relative isotopic mass: isotopic mass of an isotope relative to 1/12 of the mean mass of an atom of the carbon 12 isotope

Question 11

explain time of flight mass spectrometry

Answer 11

ionisation - a sample of an element is vaporised and injected into a mass spectrometer where high voltage is passed over the chamber causing electrons to be removed from the atoms resulting in a +1 charged ion

acceleration - positively charged ions are accelerated towards negatively charged detection plate

ion drift - ions are deflected by magnetic field into a curved path. This depends on the charge and mass of the ion.

detection - when the positive ions hit negatively charged detection plate they gain an electron producing a flow of charge

Analysis - current values used with combination of flight time to produce a spectra print out of the relative abundance of each isotope.

Question 12

what is ionisation energy

Answer 12

minimum energy required to remove one mole of electrons from one mole of atoms in gaseous state.

Question 13

trend of ionisation energy across period and down a group

Answer 13

Along a Period - first ionisation energy increases due to a decreasing atomic radius and greater electrostatic forces of attraction.

Down a Group - first ionisation energy decreases due to an increasing atomic radius and electron shielding which reduces the effect of the electrostatic forces of attraction.

Question 14

three rules for writing out electron configuration

Answer 14

lowest energy orbital is filled first
electrons with same spin fill up an orbital before pairing
no more than 3 electrons

Question 15

when does an atom become very unstable

Answer 15

if electron spins are unpaired they are therefore unbalanced producing natural repulsion between the electrons making the atom very unstable

Question 16

what is periodicity

Answer 16

when elements across the periods show repeating patterns in chemical and physical properties

Question 17

what is second ionisation energy

Answer 17

energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 18

state number of orbitals in
s
p
d
f

Answer 18

s : one orbital (1 x 2 = total of 2 electrons)

p : three orbitals ( 3 x 2 = total of 6 electrons)

d : five orbitals (5 x 2 = total of 10 electrons)

f : seven orbitals (7 x 2 = total of 14 electrons)

Question 19

explain why the ionisation energy of hydrogen is less than helium but greater than lithium

Answer 19

He more protons than H / He greater nuclear charge than H
(1)

in helium the outer electron is in the same shell as hydrogen
(1)

H > Li:
* in lithium the outer electron is in a higher energy level / a new shell / further from the nucleus / in a 2s orbital

• (and) is shielded by inner electrons / 1s? electrons

Question 20

explain why successive ionisation energies increase

Answer 20

the same number of protons is attracting a decreasing number of electrons

electron is removed from an increasingly positively charged

Question 21

explain how the giant atomic structure of silicon allows it to have a high melting point

Answer 21

(the electron being removed from E) is from a new subshell / p-subshell / p-orbital
(1)

which is more shielded from the nucleus than the s-subshell (from which the electron is removed in D)
OR
* which is further from the nucleus than the s-subshell / orbital

Question 22

why does potassium have lower ionization energy than argon

Answer 22

Alkali metals always have the lowest first ionization energy in their period

Ionization energy falls (significantly) at the start of a (new) period