THE PERIODIC TABLE

HISTORY In 1869, Mendeleev studied the 63 known elements. Mendeleev grouped elements together with similar properties, and arranged the elements by increasing atomic mass. Mendeleev detected patterns that led him to develop the periodic table. Periodic means having a regular, repeating pattern. Dmitri Mendeleev

Periods: Rows on the Periodic Table All of the elements in a period have the same number of electron shells or energy levels. The elements in the first period (top row – red) have one electron shell – the K shell. The elements in the second period (orange row) have two electron shells – the K and L shells. The elements in the third period (yellow row) have three electron shells – the K, L, and M shells. At this time, the maximum number of electron orbitals or electron shells for any element is seven. THE PERIODIC TABLE – DEFINITIONS

Groups or Families: Columns on the Periodic Table The elements in a group have the same number of electrons in their outer (valence) orbital. The elements in the first column (group one – red squares) have one electron in their valence shells. The elements in the second column (group two – orange squares) have two electrons in their valence shells. There are some exceptions to this order when you look at the transition elements (the white squares in the center of the table). Elements in the same group or column have similar chemical properties. THE PERIODIC TABLE – DEFINITIONS

CLASSES OF ELEMENTS Metals Most of the elements on the periodic table are metals. Most metals are solids. Metals tend to be shiny, malleable, ductile, and good conductors of electricity. Nonmetals More than half of the nonmetals are gases. Nonmetals typically are not shiny, not malleable, not ductile, and are poor conductors of electricity. Metalloids Metalloids are also known as semiconductors. Metalloids have some properties of metals and some properties of nonmetals. There are only 6 commonly identified metalloid elements.

Metals – Blue, Nonmetals – Yellow, Metalloids - Green

READING THE PERIODIC TABLE Atomic Number: number of protons in atom Chemical Symbol: One or two letters, the first letter is capitalized Background color: indicates metal, non- metal, or metalloid Color of symbol: indicates state (solid, liquid, gas) of element at room temperature Atomic Mass: average number of protons and neutrons in each atom.

PERIODIC TABLE - GROUPS Groups (or families) are columns on the periodic table. Elements in the same group or family have similar properties. The properties are similar because elements in the same group have the same number of electrons in their valence (outer) shell.

GROUP 1: ALKALI METALS Group 1 – Alkali Metals One electron in valence (outer) electron shell Most reactive metals They are so reactive that they are only found combined to other elements in nature Soft, silver-colored, shiny, low density Li, Na, K, Rb, Cs, Fr Does NOT include Hydrogen (H)

WHAT ABOUT HYDROGEN? The properties of hydrogen do not match the properties found in any other group or family on the periodic table Hydrogen is placed above Group 1 on the periodic table, because it has one electron in its valence (outer) electron shell Hydrogen is the most abundant element in the universe Colorless, odorless gas with a low density Reacts explosively with oxygen to form water vapor

GROUP 2: ALKALINE EARTH METALS Group 2 – Alkaline Earth Metals Two electrons in valence (outer) electron shell Not as reactive as Group 1 (Alkali Metals), but still very reactive Silver-colored, more dense than Alkali Metals Be, Mg, Ca, Sr, Ba, Ra Calcium, Beryllium, Magnesium Alkaline Earth Metals

GROUPS 3–12: TRANSITION METALS Transition Metals Groups 3 through 12 do not have individual names – they are simply referred to as the transition metals. One or two electrons in the valence (outer) shell. Less reactive than alkali metals and alkaline earth metals. Shiny, good conductors of heat and electricity, with higher densities than elements in Groups 1 & 2.

LANTHANIDE AND ACTINIDE SERIES There are two rows at the bottom of the periodic table, called the Lanthanides and Actinides They are placed at the bottom of the periodic table to keep the table from being too wide. The properties of the elements in each row are very similar. Lanthanides – shiny reactive metals Actinides – radioactive, elements heavier than plutonium (Pu) are not found in nature (lab-created)

GROUPS 13 – 16: GROUPS WITH METALLOIDS Each of these groups are named for the first element in each group: Group 13 – Boron Group Contains aluminum (Al), the most common metal in Earth’s crust. Group 14 – Carbon Group Contains carbon (C), which is an element essential to all living things. Group 15 – Nitrogen Group Contains nitrogen (N), which makes up about 78% of Earth’s atmosphere. Group 16 – Oxygen Group Contains oxygen (O), which makes up about 20% of Earth’s atmosphere.

GROUP 17: HALIDES Group 17 – Halides The halides are all nonmetals Most reactive nonmetals They are so reactive that they are only found combined to other elements in nature. Poor conductors of electricity, react violently with alkali metals to make salts. F, Cl, Br, I, At

GROUP 18: NOBLE GASES Group 18 – Noble Gases Nonmetals Unreactive The noble gases have full valence (outer) electron shells Colorless, odorless gases Naturally found in Earth’s atmosphere in small amounts Argon (Ar) is the most common noble gas, and it makes up only 1% of Earth’s atmosphere.