A2 Flashcards
how is the periodic table arranged?
-Shows all the chemical elements arranged in increasing atomic number chemists use it to predict how elements will behave or what physical/chemical properites of the element they may be
-Groups vertical columns
-Periods horizontal rows
what is period one?
what is period two?
-Period one contains hydrogen and helium (both are gases).They both fill the 1s orbital.Helium only has two electrons and chemically helium is unreactive.Hydrogen loses or gains an electron and so can behave chemically as both a group 1 and a group 7 element.Hydrogen can form compounds with most elements and is the most abundant chemical element in the universe
Period 2- contains 8 elements lithuim etc.The outer electrons in these elements fill the 2s and 2p orbitals.Nitrogen oxygen and fluorine can all form diatomic molecules.Neon is a noble gas.Carbon is a giant molecular structure
what is period 3?
what is period 4?
Period 3 - contains 8 elements eg sodium magnesium etc.Outer electrons in these elements fill the 3p and 3s orbitals
Period 4 - contains 18 elements from potassium to kyrpton.The first row of the transition elements is in this period.Outer electrons on these elements fill the 4s 4p and 3d orbitals
what block is group 1 and 2 in?
what block is gorup 3 to 7 and group 0?
-group 1 and 2 is S BLOCK
-group 3 to 7 and group 0 is P BLOCK.This block contains all non-metals except for hydrogen and helium.
-Transition metals are D BLOCK
-They arranged in these blocks to show orbital that has the highest energy electron
ATOMIC RADIUS
when does the radius of an atom change?
how do we measure the radius?
when does the atomic radius decrease in period and in group?
explain the trend for the transition metal?
-changes depending on what is around it
-we measure radius is to measure the distance between the nuclei of 2 touching atoms and divide by 2
-atomic radius decrease across the period from left to right
-across the group more protons and electrons are added however extra electrons are added to the same s and p sub shells and so the size does not increase.Extra protons increase nuclear charge.The increased nuclear charge attracts extra electrons and pulls them closer to the nucleus.This leads to a decrease in atomic radius
-As you go down the group atomic radii increases.This is because the extra electrons are added to additional shells and so the radius increases.Although nuclear charge increases number of inner shells increases and so the nuclear charge is shielded more.This means that the atomic radius increases
-Different for transition metals atomic radii get slightly smaller as you go across the start of the transition metal but then the radi stay very similar.Because the additional nuclear charge is balanced by extra shielding by the 3d electrons of the out 4s sub shell
IONIC RADIUS
what does ionic radius follow down a group?
what is the ionic radius for the cations across the period?
what is ionic radius for the anions across the period?
-Down a group increases because the extra electrons are added to extra shells as you go down the group therefore giving a larger size
-cations have a smaller radius.As you go across the period cations all have the same electronic structure,They have the same number of electrons (isoelectronic) nuclear charge increase eg mg^+3.However the number of protons increase across the period this pulls the electrons more strongly to the centre of the ion so the ionic radii of the cations decreases as you go across the period.
-anions have a larger radius.More repulsion between extra electrons.As you go across the period anions are isoelectronic for example N^3-.They have more electrons.Number of protons increase as you go across the period while the number of shells and electrons stay the same so overll is decreases as you go across the period
-ANIONS NEGATIVE
-CATIONS POSITIVE
Electronegativity
what is electronegativity?
does it increase across a period?
does it decrease down a group?
what is the most electrongegative element?
what do group 0 gases not form?
what does elecronegativity depend on?
what happens as we go across the period?
what happens as we go down a group in depth?
-Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons
-Increases across a period
-Decreases down a group
-fluorin is the most electronegative electron
-Group 0 gases such as argon do not form bonds so they don;t have electronegativity that can be reliably determined
-electronegativity depend on number of protons in the nucleus,distance from the nucleus of the bonding pair of electrons and how much shielding there is from inner electrons
-As we go across the period bonding pair of electrons will be shielded by the same number of electrons however the number of protons will increase so group 7 will be more electronegative than group 1
-As we go down a group there is more shielding from inner electrons and the bonding pair of electrons are further from the nucleus so this is less pull on bonding pair from positive charge decreasing the electronegativity
what is first ionisation energy?
-First ionisation energy is the miniuim energy needed for 1 mole of the outermost electrons to be removed from 1 mole of atoms in a gaseous state
-One mole of positively charged ions is formed
Trends down a group:
-as group goes down the first ionisation energy decreases this because the outer electron being removed is further from the nucleus and there is more inner shells to shield the outer electrons.This means the electrostatic attraction to the nucleus is less eg M (g) —M^+ (g) +e-
Trends across the period:
-increases across the period because the nuclear charge increases but the shielding due to the inner shells stays the same.This means the electrostatic attraction of the nucleus to the outer electrons increases
what is electron affinity?
explain how it decreases down a group?
-The ability as an atom to gian an electron and become a negative ion
-First electron affinity is when a -1 ion is formed.First electron affinities are negative
-equation x (g) + e- = X-
-First electron affinity deccreases down a group as the shell to which the electron is being added is further from the nucleus and has more shielding from inner shells
types of bonding in the element
what is the electronegativity of elements hydrogen?
what is bonding?
what does the extent of polarisation depend on?
-Bonding is a spectrum from ionic to covalent bonding
eg in a hydrogen molecule both hydrogen have the same electronegativiity this means they form a covalent bond which is not polar when hydrogen bonds with fluorine they form hydrogen fluoride a polar covalent is formed.This is because fluorine has a high electronegativity and so attracts the bonding oaur this gives the fluorine atom a positive charge and hydgrogen atom a negative charge
The extent of polarisation depends on ionic bonds can also show polarity:
-ion is highly charged
-cation is relatively small
-anion is relatively large
Melting points and Boiling points
what is the melting point /boiling as you go across a period between group 1 to 4 then decrease across groups 5 to 0?
-As you go across a period the melting poitns tend to increase across groups 1 to 4 then decrease across groups 5 to 0
and the boiling point is the same x
-Melting and boiling points increase in metals because of the metallic bond strength increases this is because the positive metalmions get smaller across the period their charge get larger and there are more delocalised electrons.There is a stronger attraction between positive ions and delocalised electrons
-Elements from group 4 eg carbon/silicon have very high melting/boiling because they have giant covalent with many strong covalent bonds
-Elements from group 5 6 7 are simple molecules they have weak london forces between them
what are the 4 physical properties of metals?
-Electrical conductivity due to the delocalised electrons which are free to move eg copper is a good conductor of electricity can be used for wires/cables
-Thermal conductivity delocalised electrons absorb heat gives them kinetic energy.Aluminium and copper are useful for saucepans/computer/radiators etc
-Malleable/ductile ductile roll over each other they can move to new positions without breaking eg aluminium is very malleable makes it useful for aluminium foil
