3.1 The Periodic Table Flashcards
What is periodicity
repeating trends in physical and chemical properties across the period
how are elements arranged in the periodic table?
- elements are arranged by increasing atomic (proton) number
- in periods showing repeating trends in physical and chemical properties
- elements are arranged in groups having similar chemical properties (due to similar outer shell electron config)
What happens to first ionisation energy across a period and why?
Across a period the nuclear charge increases,
so the atomic radius decrease
the shielding stays the same
so the nuclear attraction increases.
This means first ionisation energy INCREASES in general across a period as more energy is needed to remove the electron due to strong electrostatic attraction
What happens to first ionisation energy down a group?
Down a group although the nuclear charge increases,
as does the shielding and the atomic radius
so the nuclear attraction decreases.
This means first ionisation energy decreases down a group as the increase in shielding and radius outweighs increase in nuclear charge as less energy is needed to remove an electron.
Define first ionisation energy
energy needed to remove 1 mol of electrons from 1 mol of gaseous atoms
Explain the variation in melting point across the periods 2 and 3 in terms of bonding and structure
For the first three elements in the period the melting point increases as the charge of the ion increases
So they are more strongly attracted to the delocalised electrons.
The 4th element in the period usually has the highest melting point as it has a giant covalent lattice.
After that the 5th,6th,7th and 8th elements have low (usually decreasing from the 5th to 8th element) as they now have simple molecular structures.
What group does the s block consist of in the periodic table?
1-2
What group does the p block consist of in the periodic table?
3-8
What group does the d block consist of in the periodic table?
Transition metals
What group does the f block consist of in the periodic table?
lanthanides, actinides
Why is there a small decrease in ionisation energy across a period between group 2 and 3?
Group 2 elements have outer shell electron in the s orbital
Group 3 elements have outer shell electron in a p orbital
P orbital has slightly higher energy then s oribital so is marginally further from nucleus.
So electrons in these orbitals ar easier to remove due to weaker attraction.
Why is there a small decrease in ionisation energy across a period between group 5 and 6?
outer electron in group 6 is spin paired in p orbital outer shell, so experience repulsion, making it slightly easier to remove.
Why does Successive ionisation energies increase each time
because an electron has been removed so the other electrons experience greater attraction from the same number of protons. This means the electrons are pulled closer to the nucleus, the atomic radius decreases and it requires more energy to remove the next electron.
There will be larger jumps when the next electron is being removed from a shell closer to the nucleus as there is a large increase in attraction.
So group 2 elements have a large increase between 2nd and 3rd ionisation energies k
What the equation for first ionisation energy of oxygen?
O(g) –> O+(g) + e-
What the equation for the second ionisation energy of oxygen?
O+(g) –> O2+(g) + e-
How can you tell which group of the periodic table an element belongs to from the successive ionisation energy graph?
Count how many electrons were removed before the first big jump
What are the properties of diamond?
since it has strong covalent bonds: -High melting point -hard (used in diamond tip tools) -vibrations travel easily through stiff lattices so its good thermal conductor -cant conduct electricity wont dissolve in any solvent
What element has similar properties to carbon and why?
silicon,
as it also forms a crystal lattice structure and each silicon atom can form 4 strong covalent bonds
What are the properties of graphite?
- Hexagonal sheets slide past each other as the layers are bonded with weak induced dipole dipole forces it’s slippery so used as a dry lubricant ad in pencils
- can conduct electricity due to delocalised electron
- high melting point
- insoluble in any solvent (covalent bonds so strong)
Whys graphite less dense then diamond?
layers are far apart compared to length of covelent bonds, so graphite is less dense and is used to make strong lightweight sport equipment.
What are the properties of graphene?
- good at conducting electricity as only one sheet so delocalised electrons can move above and below quickly
- delocalised electron strengthen covalent bonds making it extra strong
- single layer of graphene is transparent and incredibly light
Describe the bonding in metals
The electron in outermost shell of a metal atom are delocalised-this leaves a positively charged cation
the metal cations are electrostatically attracted to the delocalised negative electrons. They form a lattice of closely packed cations in a sea of delocalised electrons
What are the properties of metals?
- high melting point effected by number of delocalised electrons
- malleable and ductile as no bonds holding specific ions together so slide past
- good thermal conductor as delocalised electrons can pass kinetic energy
- good electrical conductors
- insoluble, except in in liquid metals, due to strong metallic bonds
what has a higher melting point: sulphur, phosphorus or chlorine
and why
sulphur
as it is an S8 molecule so the more atoms mean stronger induced dipole dipole forces
Why do noble gases have very low melting points?
they exist as individual atoms resulting in very weak induced dipole dipole forces
does reactivity increase down group 2?
yes
group 2 metal + water gives?
metal hydroxide + hydrogen
Ca(s) + 2H2O(l) –> Ca(OH)2(aq) + H2(g)
be exception
group 2 metal + oxygen gives?
metal oxide
(solid white oxide)
2Mg(g) + O2(g) –> 2MgO(s)
group 2 metal + dilute acid (HCl)
metal chloride + hydrogen
Why do oxides form more strongly alkaline solutions as you go down group 2?
the hydroxides get more soluble
group 2 metal oxide + water gives?
metal hydroxide
MO(s) + H2O(l) –> M(OH)2(aq)
magnesium oxide is an exception-it only reacts slowly and the hydroxide isn’t very soluble
Group 2 redox reaction
M–> M2+ + 2e-
Soluble hydroxides release OH-
to form alkaline solutions, of roughly what pH?
pH 10-12
Which group 2 metal oxide isn’t soluble?
BeO
What are group 2 elements also known as?
Alkaline earth metals
What is calcium hydroxide, slacked lime Ca(OH)2, used for?
Used in agriculture to neutralise acidic soils
What is Magnesium hydroxide, Mg(OH)2, and calcium carbonate, CaCO3, used for?
used in indigestion tablets as antacids
Mg(OH)2 + 2HCl –> 2H20 + MgCl
What’s the ionic equation for neutralisation reaction?
H+ + OH- –>H20
What type of molecules are halogens?
Diatomic
What is the trend in reactivity down group 7?
in terms of ease of forming 1- ion
Outer shell of halogens gets further from the nucleus down the group
• Electrostatic attraction with the nucleus is lower
• Electron shielding due to inner shells is higher
• Weaker attraction to electrons
• Worse oxidising agents
• Less likely to form 1- ion
How can you see relative oxidising strengths of halogens?
Through displacement reactions with halide ions.
More reactive halogen displaces less reactive halogen
Colour change is observed
How can colour changes in displacement reaction be made easier to see?
Mix with organic solvent like hexane solution
The halogen that’s present will dissolve in it which settles out as a distinct layer above the aqueous solution
What colours are F2 Cl2, Br2, I2
F2. yellow
Cl2, green
Br2, brown
I2, grey
What is disproportionation
Simultaneous Oxidation and reduction of the same element
Give 2 example equations for disproportionation
Chlorine with water
Chlorine with cold dilute NaOH(aq)
Cl2 + H2O –> HCl + HClO (water treatment)
Cl2 + 2NaOH –> NaCl + NaClO + H2O (Forms bleach)
Aqueous chloric(I) acid ionises to make chlorate(I) ions (aka hypochlorite ions) Whats the equation for this?
HClO (aq) + H20 (l)–>CLO-(aq) + H30+ (aq)
Why’s chlorine used in water treatment?
- Kills disease causing microorganisms
- some chlorine remains to prevent reinfection further down supply
- It prevents the growth of algae, eliminating bad taste and smell and remove discolouration caused by organic compounds
What are the risks and issues of using chlorine to treat water?
- Chlorine gas Irritates respiratory system, liquid can cause chemical burns
- Water contains organic compounds which chlorine reacts with forming chlorinated hydrocarbons, This increases cancer risk
- ethical considerations as “forced mass medication”
What are alternatives to using chlorine in water treatment?
Ozone- strong oxidising agent kills microorganisms, but expensive and short half life in water so not permanent treatment
UV Light- Kills microorganisms by damaging DNA, but ineffective in cloudy water, like 03, it wont stop water contamination down the line
Whats the test for halides?
Add dilute nitric acid (to remove ions that may interfere)
Then add silver nitrate solution
Precipitate formed
To be extra sure add ammonia solution
What colour precipitate does Cl, Br, and I form? and whats there solubility in ammonia?
Cl- is White precipitate, dissolves in dilute NH3
Br- is Cream precipitate, dissolves in concentrated NH3
I- is Yellow, insoluble in concentrated NH3
To test for carbonate…
- Add a strong dilute acid
- Pass any gas formed through lime water
- if it goes cloudy carbonate is present
Carbonate reacts with acid to form CO2
What’s the ionic equation?
CO3 2-(aq) + 2H+(aq) –> H2O(l) + CO2(g)
Sulfate reacts with barium ions to form an insoluble salt. Whats the ionic equation?
Ba2+(aq) + SO4 2-(aq) –> BaSO4(s)
To test for sulfate ions…
- Add HCl and barium chloride
- If a white precipitate forms barium ions are present
Ammonium ions react with hydroxide to form ammonia and water.
Whats the ionic equation?
NH4+ (aq) + OH- (aq) –> NH3(g) + H2O(l)
To test for ammonium…
- Add NaOH solution and warm gently
- Test any gas involved with litmus paper
- If it goes blue and the gas smells like ammonia when wafted gently towards your nose, ammonia is present
To avoid mix ups what order should you do the tests in?
Test for carbonates…If no C02
Test for sulphates… If no precipitate
Test for Halides
explain why ZnCl2 is a salt
H+ (of hydrochloric acid) are replaced by Zn2+
What is meant by a giant covalent lattice?
networks of atoms bonded by strong covalent bonds
