2.2 PERIODIC TABLE AND CHEMICAL PROPERTIES BC Science 9: p

PERIODIC TABLE Chemists in the tenth century wished to organize elements. Attempts focussed on grouping elements with similar properties. In 1867, Dimitri Mendeleev found patterns in the elements and organized them into a table. The resulting table had holes for elements not discovered yet.

PERIODIC TABLE The periodic table provides information on the physical and chemical properties of elements. Atomic Number: Increases from left to right and from top to bottom. Equal to number of protons in the atom.

PERIODIC TABLE Ion Charge: Electric charge when atoms gain or lose electrons. Atoms that lose electrons form positive ions. Atoms that gain electrons form negative ions. Elements on the left form positive ions. Elements on the right form negative ions.

PERIODIC TABLE Atomic Mass: The mass of an average atom of the element. Measured in atomic mass units (amu) The number of protons and the number of neutrons added together equals the atomic mass. Atomic mass generally increases with atomic number.

Metals, Non-metals, Metalloids There are many patterns in the periodic table. Due to Mendeleev’s organization, interesting patterns such as the groups: metals, non-metals and metalloids. Metals are found on the left. Non-metals are found on the right. Metalloids (ie. semi-metals) are found along the staircase.

Metals, Non-metals, Metalloids

Periods and Families Each horizontal row in the periodic table is a period. Vertical columns form groups or chemical families.

Notable Families

Notable Groups Group NumberGroup NameProperties 1Alkali MetalsHighly reactive metals 2 Alkaline Earth Metals Burn in air if heated 17HalogensHighly reactive non-metals 18Noble GasesStable and unreactive non-metals

Group 1: Alkali Metals Highly reactive and reactivity increases from top to bottom. React with both oxygen and water. Low melting points < 200°C. Soft and can be cut with a knife. Form +1 ions.

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Group 2: Alkaline Earth Metals Less reactive than alkali metals but will burn if heated. Produce bright flames and are used in fireworks. React with water, but not as vigorously as alkali metals. Reactivity increases from top to bottom. Form +2 ions.

Group 17: Halogens Highly reactive and reactivity increases from bottom to top. At room temperature, fluorine and chlorine are gases, bromine is liquid and iodine is solid. Astatine is extremely rare and little is known about it. Form -1 ions.

Group 18: Noble Gases The most stable and unreactive elements in the periodic table. Colourless, odourless gases at room temperature. Some glow as distinct colours with electricity eg. neon and argon Helium is lighter than air. Do not form ions.

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