Periodic Table (Pre-IB SC 9)
What is the periodic table, and approx. how many elements are identified?
The periodict table is an organized chart containing information about the atoms that make up all matter. An ELEMENT is made up of only one atom, and there are currently 118 identified elements.
Properties of metals vs non-metals vs semi-metals (metalloids)
Metals: Durable, solid, good conductors, malleable, and lustrous
Non-metals: Not durable, brittle solid, insulators, not malleable, and not lustrous.
Semi-metals: Not durable, not ductile, not malleable, semi-conductive, and lustrous
Which direction does a PERIOD go, and what does that tell us about electron shells?
A period goes horizontally across the table, and the period number indicates the number of electron shells (AKA orbitals) containing electrons.
Which direction does a GROUP go? What does this tell us about valence electrons?
A group goes vertically down the table, and the group number (exlcuding the transition metals) indicates the number of valence electrons in the outermost shell.
What is the trend of atomic size going down and across the table?
The atomic size INCREASES moving down a group because the elements have an increasing number of electron shells or energy levels. Shielding increases as the number of energy levels increases, which decreases effective nuclear charge and weakens the nucleus's pull or "grip" on the electrons, resulting in a bigger atomic size.
The atomic size DECREASES moving left to right across a period because elements have increasing numbers of valence electrons BUT the number of occupied valence shells stays the same. The effective nuclear charge increases while electron shielding remains constant, so the nucleus pulls the electrons tighter to the nucleus.