2.2 The Periodic Table

The Periodic Table Every block represents an element Every periodic table has a key

The Periodic Table Where did the modern periodic table come from? Newlands Newlands Mendeleyev Mendeleyev

Modern Periodic Table Period or Series – a horizontal row of elements, numbered 1-7) Group or Family – a vertical row of elements (numbered 1-18 on the modern table) (long ago: roman numerals)

Modern Periodic Table Staircase – divides the metals from the nonmetals Metalloids – look like metals but act like nonmetals

The Periodic Law States that when elements are arranged in order of increasing atomic mass, certain physical and chemical characteristics repeat in a regular pattern (periodically)

Modern Periodic Table Atomic Mass – defined relative to the mass of a carbon atom, which is given a mass of 12 amu AMU (atomic mass unit) – defined as 1/12 the mass of a carbon atom

Period / Group Names Group 1 – Alkali Metals Soft, silver colored metals that react violently with water Soft, silver colored metals that react violently with water React with the halogens React with the halogens Group 2 – Alkaline Earth Metals Light, reactive metals that form oxide coatings with air exposure (ex MgO, CaO) Light, reactive metals that form oxide coatings with air exposure (ex MgO, CaO)

Period / Group Names Group 17 – Halogens Extremely reactive (F is the most) Extremely reactive (F is the most) Form hydrogen halides (ex HCl) Form hydrogen halides (ex HCl) Group 18 – Noble Gases Extremely low chemical reactivity Extremely low chemical reactivity

Period / Group Names Transition Elements Groups 3-12 Groups 3-12 Representative Elements Groups 1-2, & Groups 1-2, & * Hydrogen is the exception to almost every rule in chemistry

The Atom

Is the smallest part of an element that is still representative of that element A neutral particle composed of a nucleus (containing protons and neutrons) and electrons # electrons = # protons

Electrons e - A small, negatively charged subatomic particle Has negligible mass

Nucleus The centre of an atom Contains most of the mass and all of the positive charge of an atom

Protons p + Positively charged subatomic particle Found in the nucleus Mass of 1 amu

Neutrons n Uncharged (neutral) Found in the nucleus Mass of 1 amu

Atomic Number and Atomic Mass Atomic Number The number of protons an atom has The number of protons an atom has Different for each element Different for each element Atomic Mass (Mass Number) # protons + # neutrons # protons + # neutrons