Chemistry - Chapter 1 + 8 - Atomic Structure/Trends in Period 3

robert boyle

proposed idea of chemical elements

john dalton

suggested that atoms were the smallest unit of matter

henri becquerel

discovered radioactivty

ernest rutherford

discovered nuclear model

Niels Bohr

atom was a positive nucleus orbited by electrons - + discovered quantum theory

james chadwick

discovered neutron

electron relative mass:

1/1840

proton + neutron mass

1

energy levels are aka as?

shells

nuclear charge is aka as?

number of protons

what are the 4 main orbitals?

S,P,D,F

how many electrons does the S orbital hold

2 - has 1 orbital

how many electrons does the p orbital hold?

6 - has 3 orbitals

how many electrons does the d orbital hold?

10 - has 5 orbitals

how many electrons does the f orbital hold?

14 - has 7 orbitals

how many electrons does 1 single orbital hold?

2

full electron configuration:

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

what determines chemical properties of an element

the electron arrangement of the atom

why is 4s lower than 3d

as it is of a lower energy shell

name a property of electrons and it’s function:

Spin - electrons in the same orbital have opposite spin to overcome the repulsion between them

what are the 3 rules for allocating electrons to orbitals?

1. Atomic orbitals of lower energy must be filled first

2. Atomic orbitals of same energy must be filled singly before pairing - because of repulsion between electrons

3. No atomic orbital can hold more than 2 electrons

what is a rule that is used when forming positive ions?

the 4s shell is dropped before the 3d shell as it is of lower energy level

what are the 2 exceptions in electron configuration - + what is their eception

chromium and copper - they would rather have full 3d shells than 4s shells as it’s more stable

ionisation energy definition

the amount of energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of unipositive ions

ionisation energy formula

X^(n-1)+(g) → Xⁿ⁺ (g) + e^-

trends in first IE across period 2/3

general trend —>

• as you go across period greater nuclear charge

• similar shielding

• lower atomic radius

• greater electrostatic f.o.a

GROUP 2 - 3 DIP

• group 3 outermost electron in new 3p orbital

• higher energy level

• more shielded

• group 3 has lower IE

GROUP 5 - 6 DIP

• group 6 electrons start to pair in a single P orbital

• repulsion between electron in orbital

• so group 6 has lower IE

trends in IE as you go down a group:

• Generally IE decreases as you go down the group

• More shells as you go down

• So more shielding as you go down

• So weaker electrostatic f.o.a as you go down

• So less energy required to remove outermost electron from gaseous atom

how is it shown that the s sub-shell can only hold 2 electrons?

as it has two elements before the IE drop

how is it shown that the p sub-shell can only account for 3 unpaired electrons

as there are 3 elements (each for one unpaired electron) before IE drop

what are the only two subatomic structures affect atomic radius?

protons → causes greater electrostatic force between nucleus and outermost electron decreasing atomic radius

electrons → the addition of electrons to the outermost shell increases radius

relative atomic mass (Ar) definition

average mass of 1 atom / (1/12) mass of 1 atom of C12

relative molecular mass (Mr) definition

average mass of a molecule / (1/12) mass of 1 atom of C12

function of mass spectrometer:

determines the mass of separate atoms/molecules

what are the 2 principles all mass spectrometers function on?

forming positive ions

separating ions according to their ratio of mass to charge

what are the 6 steps in TOF mass sepctrometery

vaccum

ionisation

acceleration

ion drift

detection

data analysis

vacuum TOF

apparatus kept under vaccum to prevent ions produced colliding with molecules of air

ionisation TOF

ELECTROSPRAY

• sample dissolved in volatile solvent and injected in hypodermic needle forming aerosol

• tip of needle attatched to positive terminal of high-voltage power supply

• particles ionised by gaining a proton forming XH^+ ion

ELECTRON IMPACTS

• sample vaporised

• high energy electrons fired from electron gun

• knocks of 1 electron from each particle forming a unipositive ion

• (may knock of 2 sometimes)

Acceleration

positive ions attracted to negatively charged plate and accelerate towards it

lighter ions/highly charged ions have a higher speed

Ion Drift

• The samples will separate according to mass → all  ions set off along the same time, lighter ions travel faster and start to separate out reaching the detector first

Detection

• positive ions hit negatively charged plate

• gain electrons from plate and are discharged

• this generates a movement of electrons (current) causing TOF to be measured

• size of current is proportion to ion abundance present

data analysis

signal from a detector is passed onto computer to form a mass spectrum

RAM formula

(isotope 1 Ar % abundance) + (isotope 2 Ar * % abundance) /100

all percentage abundances of isotopes for an elements add up to…

100%

mass formula

RAM/ avagadro’s constant

reactivity in S-block

increases as you go down the group

reactivity in non-metals

increases as you go up the group

group 1-3 (period 3) features

• metals

• ionic bonding

• giant ionic structure

• S-block

group 1-3 m.p/b.p

• giant structures so have high melting/boiling points

• melting point increases from sodium to aluminium as metallic bonding strength increases

• ion charge increases so more electrons join sea of delocalised electrons which hold lattice together

why does atomic radius decrease as you go across a period?

• as you go across period greater nuclear charge

• so increased charge increases electrostatic f.o.a between nucleus an outermost electrons

• similar shielding

• so atomic radii decreases as you go across