Periodic Table & Trends - Leaving Cert Chemistry

element

a simple substance that cannot be broken into anything simpler

triad

dobereiner, elements with similar chemical properties in groups of three, middle element’s atomic weight is halfway between the other two

octave

newlands, arranged elements in order of atomic weights, every 8th repeated properties

periodic law

when elements are arranged in order of atomic weight, their properties vary periodically

atomic number

number of protons in an atom of that element

mass number

average mass of the isotopes of that element

isotope

atoms of the same element (atomic number) with different mass numbers due to differet numbers of neutrons in the nuclei

relative atomic mass

the average mass of the isotopes of that element, taking their abundance into account, compared to the carbon 12 isotope

aufbau principle

electrons always occupy the lowest available energy level first

hunds rule

where two or more orbitals are available, electrons will occupy them singly before filling them in pairs

pauli exclusion theory

no more than two electrons may occupy an orbital and they must have opposite spin

atomic radius

half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond

first ionisation energy

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

second ionisation energy

the energy required to remove the most loosely bound electron from a positive ion, Be+ → Be2+ + e-

electronegativity

a measure of the relative attraction an atom of an element has for the shared pair of electrons in a single covalent bond

dobereiner

triads

humphry davy

passed electric current through a number of compounds. compounds split into their component elements.

robert boyle

defined element

newlands

octaves

mendeleev

periodic law, periodic table

mendeleev vs. modern

mendeleev - in order of atomic weight, modern - in order of atomic number, mendeleev - gaps for undiscovered elements, modern - no gaps

mosely

used xrays to discover numbe of protons, placed elements in order of atomic number

mass spectrometer - vapourisation

the sample turned into a vapour or a gas

mass spectrometer - ionisation

electrons removed from the atoms to form positive ions

mass spectrometer - acceleration

through a magnetic field

mass spectrometer - separation

the ions are separated according to their mass

detection

both the type and the abundance of each type of ion is detected

atomic radius - increase - down group

addition of new energy level, screening effect of inner electrons

atomic radius - decrease - across period

increase in nuclear charge, no increase in screening effect

first ionisation energy - decrease - down group

increasing atomic radius, screening effect of inner electrons

first ionisation energy - increase - across period

increasing nuclear charge, decreasing atomic radius

reactivity of alkali metals - increase - down group

increase in atomic radius, increase in shielding, decrease in ionisation energy

reactivity of halogens - decrease - down group

increase in atomic radius, increase in shielding

electronegativity - decrease - down group

increasing atomic radius, screening effect of inner electrons

electronegativity - increase - across period

increasing nuclear charge, decreasing atomic radius