LC CHEMISTRY- TRENDS IN THE PERIODIC TABLE

REBECCA'S LC CHEMISTRY- TRENDS IN THE PERIODIC TABLE KNOWT

atomic radius

half the distance between the nuclei of two bonded atoms

increase

atomic radius values increase down the groups in the periodic table

reasons for increasing atomic radius

• new energy levels

• screening effect of inner electrons

screening effect

inner electrons shield outer electrons from the nucleus's positive charge

decrease

atomic radius values decrease across a period in the periodic table

reasons for decreasing atomic radius

• increased effective nuclear charge

• no increased screening effect

first ionisation energy

the minimum energy required to remove the most loosely bound electron from a neutral gaseous atom in its ground state

decrease

first ionisation energy decreases down a group in the periodic table

reasons for decreasing first ionisation energy

• increasing atomic radius

• screening effect of inner electrons

increase

first ionisation energy increases across a period in the periodic table

reasons for increasing first ionisation energy

increasing effective nuclear charge and decreasing atomic radius

second ionisation energy

the energy required to remove an electron from a monopositive ion in the gaseous state

electronegativity

the relative attraction an atom in a molecule has for the shared pair of electrons in a covalent bond

decrease

electronegativity decreases down the groups in the periodic table

reasons for decreasing electronegativity

• increasing atomic radius

• screening effect of inner electrons

increase

electronegativity increases across the periods in the periodic table

reasons for increasing electronegativity

increasing effective nuclear charge and decreasing atomic radius

chemical reactivity of alkali metals

• increases down the group

• they are very reactive with low first ionisation energy

oxide

forms when an alkali metal reacts with oxygen

hydroxide

forms when an alkali metal reacts with water

chemical reactivity of halogens

• halogens are the most electronegative element

• reactivity decreases down the group

state change of halogens

• fluorine and chlorine are gases

• bromine is a liquid

• iodine is a solid at room temperature

trend in energy levels moving down a group

increases

trend in energy levels moving across a period

stays the same

trend in shielding effect moving down a group

increases

trend in shielding effect moving across a period

no change

trend in atomic radius down a group

• increases due to extra energy levels

• increased shielding effect

trend in atomic radius across a period

• decreases due to increased nuclear charge

• no increased shielding

equation for first ionisation of sodium

NA → NA+ + e-

equation for second ionisation of magnesium

MG+ → MG2+ + e-

monopositive ion

an ion with one positive charge

dipositive ion

an ion with two positive charges

general trend in first ionisation energy down a group

decreases

reasons for decreasing first ionisation energy down a group

• increasing atomic radius

• screening effect

general trend in first ionisation energy across a period

increases

reasons for increasing first ionisation energy across a period

• decreasing atomic radius

• increasing effective nuclear charge

why lithium's first ionisation energy is higher than sodium's

• lithium has a smaller atomic radius

• less shielding

why chlorine's first ionisation energy is higher than sodium's

• chlorine has a smaller atomic radius

• higher nuclear charge

evidence for energy levels from ionisation energies

large spikes between groups of ionisations show electrons in different energy levels

why noble gases have no electronegativity values

they do not form covalent bonds

group 1 elements - electron configuration

one electron in the outer shell

group 7 elements - electron configuration

seven electrons in the outer shell

group 0 elements - electron configuration

full outer shell

reactivity comparison: lithium vs sodium

sodium is more reactive

reactivity comparison: chlorine vs bromine

chlorine is more reactive

inert

unreactive

why noble gases are inert

• full outer shells

• no need to gain or lose electrons

displacement reaction

a more reactive element replaces a less reactive element in a compound

why KBr + I2 does not react

iodine is less reactive than bromine

why fluorine is more reactive than chlorine

• fewer energy levels

• less shielding

why potassium is more reactive than lithium

lower first ionisation energy

why bromine is less reactive than chlorine

more shielding and a larger atomic radius

why sodium is less reactive than caesium

higher first ionisation energy

balanced equation for potassium and water

2K + 2H2O → 2KOH + H2

name LiOH

lithium hydroxide

name KOH

potassium hydroxide

why group 1 elements are called alkali metals

they form alkalis when reacting with water