C15 : The Periodic Table

Txt. P. 436-437 – Periodic Table Read the uses of elements from the text

Q: What is the purpose of periodic table ? A: To arrange all the elements in order according to their properties.

In modern periodic table, we arrange elements in terms of atomic no. Q: What are the advantages of using atomic no. to arrange the elements? A: 1) all atoms within an element have the same atomic no. 2) each element has its own atomic no. →no 2 elements have the same atomic no. → no 2 elements will occupy the same element key.

Properties of the Periodic Table Row : period Column : group / family The elements in the same group have similar chemical properties Example : G1 elements react violently with water. Demo : sodium with water

Representative elements – G1-2, G13-18 Transition elements – G3-12 Inner transition elements – Lanthanides and Actinides

Elements 93 and above have been created artificially All elements in the periodic table can exist in all 3 states. The states in the periodic table is at room temp. and standard atm. press. Chemical properties, not physical properties, determine an element’s location in the table.

An element’s properties can be predicted from its location in the periodic table. 18 groups and 7 periods As you move across a period from left to right, the properties of elements change according to a pattern.

Example : In 4th period, elements change from very reactive metals such as K and Ca →relatively less reactive metals, such as Ni and Cu →metalloids such as Ge→non-metals such as Br. The last element in the period (or G18) is always an inactive gas.

Periods have different no. of elements Example : P1 has the least no. of elements P6 & 7 have most no. of elements (32 each) 1st period →1 shell 2nd period → 2 shells

G1 : 1 valence electron G2 : 2 valence electrons G13 : 3 valence electrons G14 – 18 : 4 – 8 valence electrons G3 – 12 : transition metals

Q : Why do the properties of elements across a period change in a regular way? A: due to valence electrons, 1 additional from left to right.

Q: Why do elements within a group share similar chemical properties? A: the elements within the same group have the same no. of valence electrons.

Metals Most of the elements in the periodic table are metals. (~75%) The rest are non-metals and metalloids (semi-metals)

Metals are determined by the following physical properties : Hardness Shininess Malleability – one that can be hammered into shapes Ductility – one that be stretched into wires or hammered into thin sheets by looking into these physical properties, chemists will decide if the element is a metal.

Other physical properties of metals : Good conductors of heat and electricity Magnetic (copper is non-magnetic) Solids at room temperature (mercury is a liquid)

Chemical properties of metals : Some metals like Na and K are very reactive metals. They combine with other elements and compounds quickly. eg : Na will react explosively if exposed to air or water. b) Other metals like Au and Cr are unreactive. eg : gold stays shiny when reacts with air or water. Cr is plated on objects left outdoors to prevent rust

c) Some metals fall in between Na and Au in terms of their reaction. eg : iron (transition metals) reacts slowly with oxygen in air to form metal oxides (rust). Metals in periodic table tend to become less reactive as you move from left to right.

Group 1 metals They are called alkali metals most reactive metals. Reactivity increases down the group never found uncombined in nature, always found in compounds but never as elements alone in nature soft and shiny silvery solids low density and low m.p lithium compounds are used in batteries and some medicines

Q: Why are G1 metals so reactive? A : They all have 1 valence electron, hence this electron is easily transferred away to form octet structure which is more stable.

Group 2 Metals They are called alkaline earth metals not as reactive as G1 Each alkaline earth metal is denser and harder and has a higher m.p than the alkali metal in the same period. found in compounds in nature 2 valence electrons – easily lose them in chemical reactions to form ionic bond fairly hard silver white

Transition Metals G3 – G12 elements in here are very similar Iron, copper, silver, gold hard and shiny stable – reacting very slowly with air and water Higher m.p (eg : tungsten - 3410°C) exception : mercury (-39°C)

G13 – G16 Include metals, non-metals and metalloids Aluminum, Tin, Lead

Lanthanides & Actinides Lanthanides (rare earths) are soft, malleable, shiny, high conductivity Usually found combined with oxygen in Earth’s crust Used in industry to make various alloys They are usually found together in nature and it is difficult to separate them because they have very similar properties Actinides : all the actinides are radioactive Uranium → produce energy in nuclear power All elements after uranium were created artificially in the lab – the nuclei of these created elements are very unstable → they decompose to give radiation

Non-metals and Metalloids located right of the zigzag line in the periodic table except Ge and Sb. physical properties of non-metals : gases at room temp (low boiling point) example : N2, O2 exception : carbon, sulfur are solids at room temp : bromine is the only non-metal which is a liq at room temp

b) dull c) solid non-metals are brittle, non malleable and not ductile d) smaller density than metals e) poorer conductors of heat and electricity

Chemical properties of non-metals They form compounds easily except G18 example : CO2, HCl Besides G18, other non-metal elements either gain or share valence electrons. They don’t lose electrons

How non-metals combine? non-metal and metal eg : NaCl non-metal and non-metal eg : CO, CO2 Identical molecules eg : O2, N2

Metalloids 7 elements both metal and non-metal characteristics Its varying ability to conduct electricity makes it useful. Its conductivity depends on : temp exposure to light presence of impurities used to make semiconductors

G13 – Boron family G14 – Carbon family 4 valence electrons G15 – Nitrogen family 5 valence electrons G16 – Oxygen family 6 valence electrons

G17 – Halogen family 7 valence electrons diatomic molecules form ionic compounds with metals G18 – noble gases they are unreactive and seldom form compounds Hydrogen : 1 proton and 1 electron, with or without neutron simplest element

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