The Periodic Table Until 1750 only 17 known elements Mainly metals -such as copper and iron

The Periodic Table In 1789 A French Chemist Lavoiser grouped known elements into groups he called metals, non-metals, gases and earths

Dmitri Mendeleev Dmitri Mendeleev (1869, Russian) Organized elements by increasing atomic mass. Predicted the existence of undiscovered elements.

Mendeleev Periodic Table In 1860 there were 63 known elements Needed a way to organize them to teach his students Inspired by the card game, “solitaire”

Mendeleev Proposal On each card he listed the elements name, mass, and properties Arranged the elements into rows in order of increasing mass In a column the masses increased from top to bottom

Mendeleev’s Prediction Could not make a complete table of the elements (many still undiscovered) Left spaces in his table for those elements

Evidence Mendeleev predicted a soft metal with a low melting point In 1875 French chemist discovered Gallium (melting point 24.7 degrees Celsius) Showed how useful the periodic table could be

Henry Mosely Henry Mosely (1913, British) Organized elements by increasing atomic number. Fixed problems in Mendeleev’s arrangement.

The Periodic Table Metals Nonmetals Metalloids

Columns & Rows Group (Family), Vertical Period, Horizontal

Periods Each row in the table of elements is a period Period 1 has 2 elements, periods 2-3 has 8 elements, periods 4-5 has 18 elements, and period 6 has 32 elements

Groups Each column on the periodic table is called a group Elements within a group have similar properties Elements of a group have similar electron configurations and chemical properties

The Periodic Table Periodic Law Properties of elements repeat periodically when the elements are arranged by increasing atomic number.

Periodic Table Atomic Mass: -is a value that depends on the distribution of an elements isotopes in nature and the masses of those isotopes -Protons plus Neutrons

Periodic Table Atomic Mass Units (amu) -Is defined as 1 / 12 the mass of a carbon – 12 atom

Classes of Elements 3 ways to classify elements -classified as solids, liquids, and gases -those that occur naturally in nature and those that do not

Classes of Elements -Puts elements into categories based on their general properties -metals, nonmetals, and metalloids

Metals Majority of elements are metals Good conductors of heat and electric current Most metals are malleable (ability to be hammered) Some reactive with other elements some do not

Nonmetals Properties opposite of metals Poor conductors of heat and electricity Low boiling points, usually gases at room temperature

Metalloids Elements with properties that fall between metals and nonmetals -EX: Graphite

Variation Across a Period Across the periodic table from left to right, the elements become less metallic and more nonmetallic in their properties

Periodic Table Valence Electrons e- in the outermost energy level Highest occupied energy level Properties vary across a period, because the # of valence electrons increases from right to left

Valence Electrons Plays a key role in chemical reactions Elements in a group (up/down) have similar properties, because they have the same number of valence electrons

Alkali Metals Elements in group 1A are called alkali metals Only have 1 valence electron and are extremely reactive Found in nature as compounds -EX: table salt, compound of sodium / chlorine

Alkaline Earth Metals Group 2A has 2 valence electrons Differences in reactivity with Alkaline Earth Metals are shown by the ways they react with water

Examples of Alkaline Earth Metals Magnesium – plays a key role in the process the uses sunlight to produce sugar in plants Calcium – your body needs calcium to keep your bones and teeth strong

The Boron Family Group 3A contains the metalloid boron and 4 metals (3 valence electrons) Most abundant metal in the earth’s crust is aluminum -Strong, light weight, malleable, and a good conductor of heat / electricity

The Carbon Family Group 4A contain 4 valence electrons Life on earth would not exist without carbon Except for water, most of the compounds in your body contain carbon

The Nitrogen Family Group 5A includes elements with a wide range of physical properties Have 5 valence electrons Nitrogen and phosphorus are the most important elements in group 5A

The Oxygen Family Group 6A has 3 nonmetals and 2 metalloids (6 valence electrons) Oxygen is the most abundant element in the earth’s crust Complex life forms need Oxygen to stay alive -Oxygen is used by the body to release the energy stored in food

The Halogens Elements in group 7A are called Halogens Has 7 valence electrons Despite their physical differences, they have similar chemical properties

The Noble Gases Elements in group 8A are called noble gases Helium has 2 valence electrons where the other noble gases has 8 Noble gases are colorless and odorless and extremely un-reactive

Periodic Trends Group # = # of valence e- (except He) Families have similar reactivity. Period # = # of energy levels 1A 2A 3A 4A 5A 6A 7A 8A

Dot Diagrams Dots represent the valence e-. EX: Sodium EX: Chlorine