THE OUTER SHELL OF AN ATOM IS CALLED THE VALENCE SHELL, AND THE ELECTRONS IN IT ARE CALLED THE VALENCE ELECTRONS. ELEMENTS IN A GIVEN GROUP HAVE THE SAME NUMBER OF VALENCE ELECTRONS, AND, AS A RESULT, HAVE SIMILAR CHEMICAL PROPERTIES. THINGS WE’VE LEARNED: 1) THE ATOMIC NUMBER IS EQUAL TO THE NUMBER OF ELECTRONS IN A NEUTRAL ATOM.

2) THE NUMBER OF SHELLS THE ATOM OF AN ELEMENT CONTAINS IS EQUAL TO THE PERIOD NUMBER. 3) FOR THE REPRESENTATIVE ELEMENTS, THE NUMBER OF VALECNE ELECTRONS IS THE SAME AS THE GROUP NUMBER. 4) FOR THE REPRESENTATIVE ELEMENTS, THE NUMBER OF ELECTRONS IN THE VALENCE SHELL INCREASES BY ONE AS YOU PROCEED ACROSS A PERIOD.

THE REPRESENTATIVE ELEMENTS ARE COLUMNS 1, 2, AND 13 TO 18. THE TRANSITION ELEMENTS ARE COLUMNS 3 TO 12. THE INNER TRANSITION ELEMENTS ARE ELEMENTS 57 TO 71 AND 89 TO 103.

9 F 19 a)What is its atomic number? Atomic mass? b)Is it a representative, transition, or inner transition element? c)What period is it in, and what is its group number? d)How many total electrons are in an atom of fluorine? e)How many valence electrons are in it? f)How many shells of electrons are in a fluorine atom? g)What is its electron configuration? h)Draw a diagram of a fluorine atom.

11 Na 23 a)What is its atomic number? Atomic mass? b)Is it a representative, transition, or inner transition element? c)What period is it in, and what is its group number? d)How many total electrons are in an atom of sodium? e)How many valence electrons are in it? f)How many shells of electrons are in a sodium atom? g)What is its electron configuration? h)Draw a diagram of a sodium atom.

13 P 31 a)What is its atomic number? Atomic mass? b)Is it a representative, transition, or inner transition element? c)What period is it in, and what is its group number? d)How many total electrons are in an atom of phosphorus? e)How many valence electrons are in it? f)How many shells of electrons are in a phosphorus atom? g)What is its electron configuration? h)Draw a diagram of a phosphorus atom.

ATOMIC RADIUS (SIZE) INCREASES AS YOU MOVE DOWN IN A GROUP. ATOMIC RADIUS DECREASES AS YOU MOVE ACROSS IN A PERIOD. AS YOU MOVE DOWN IN A GROUP, EACH PERIOD REPRESENTS AN ADDITIONAL SHELL, SO THE VALENCE (OUTER) ELECTRONS ARE FURTHER FROM THE NUCLEUS AND HAVE ADDITIONAL SHIELDING. AS YOU MOVE ACROSS IN A PERIOD, NUCLEAR CHARGE IS INCREASING, AND THE ELECTRONS ARE GOING INTO THE SAME SHELL.

Atomic radius vs. atomic number

IONIZATION ENERGY IS THE ENERGY REQUIRED TO REMOVE AN ELECTRON FROM A ATOM. IN GENERAL, IONIZATION ENERGY INCREASES AS YOU MOVE ACROSS A PERIOD, AND IT DECREASES AS YOU MOVE DOWN IN A GROUP. AS YOU MOVE ACROSS IN A PERIOD, ATOMIC SIZE IS DECREASING AS IS NUCLEAR CHARGE. AS YOU MOVE DOWN IN A GROUP, ATOMIC SIZE IS INCREASING.

Ionization energy vs. atomic number

ELECTRON AFFINITY IS THE ENERGY RELEASED WHEN A NEUTRAL ATOM GAINS AN ELECTRON. YOU CAN SORT OF THINK OF IT AS BEING THE REVERSE OF IONIZATION ENERGY – RATHER THAN HOW EASILY AN ATOM CAN LOSE AN ELECTRON TO HOW EASILY AN ATOM CAN GAIN AN ELECTRON. AS YOU MOVE ACROSS IN A PERIOD, ELECTRON AFFINITY INCREASES, AND AS YOU MOVE DOWN IN A GROUP, ELECTRON AFFINITY DECREASES.

IONIZATION ENERGY AND ELECTRON AFFINITY RELATE TO THE KINDS OF ELEMENTS WE DEAL WITH. METALS ARE ELEMENTS THAT CAN EASILY LOSE ELECTRONS IN CHEMICAL REACTIONS. NON METALS ARE ELEMENTS THAT CAN EASILY GAIN ELECTRONS IN CHEMICAL REACTIONS. THESE GIVE THE ELEMENTS CERTAIN SPECIAL PROPERTIES.

ATOMS CAN GAIN OR LOSE ELECTRONS TO FORM IONS – AN ATOM OR GROUP OF ATOMS WITH A CHARGE. IF AN ATOM LOSES AND ELECTRON(S) IT BECOMES POSTIVELY CHARGED. IF AN ATOM GAINS AN ELECTRON(S) IT BECOMES NEGATIVELY CHARGED.

METALS 1.METALS TEND TO HAVE LOW IONIZATION ENERGIES AND TEND TO FORM POSITIVE IONS 2.HAVE A SHINY LUSTER AND MOST ARE SILVERY 3.SOLIDS ARE MALLEABLE AND DUCTILE 4.GOOD CONDUCTORS OF HEAT AND ELECTRICITY

NONMETALS 1.NONMETALS HAVE HIGH ELECTRON AFFINITIES AND TEND TO GAIN ELECTRONS TO FORM NEGATIVE IONS. 2.DO NOT HAVE A LUSTER. 3.SOLIDS ARE USUALLY BRITTLE. 4.POOR CONDUCTORS OF HEAT AND ELECTRICITY.

NOTE THAT MOST ELEMENTS ARE METALS.