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Chemistry-Atomic Structure and the Periodic table (The Periodic Table (The…
Chemistry-Atomic Structure and the Periodic table
Atoms, Elements, Compounds and Mixtures
An element is a substance that contains only one sort of atom. There are 100 different elements.
A compound is 2 or more elements, chemically bonded
A mixture is 2 or more elements, not chemically bonded
Compounds can only be separated into their component elements by chemical reactions or electrolysis
Scientists use chemical formulae to show:
-the different elements in a compound
-how many atoms of each element one molecule of the compound contains
Equations
-the reactants(the substances that react) are on the left hand side of the equation
-the products(the new substances that are formed) are on the right hand side of the equation
The total mass of the products of a chemical reaction is always equal to the total mass of reactants. This is because no atoms are lost or made.
Separating Mixtures
Mixtures can be separated by physical processes- these processes do not involve chemical reactions, so no new substances are made
Filtration
-separate soluble liquids from insoluble liquids
Crystallisation
-used to obtain a soluble solid from a solution, (1. Mixture is warmed, 2. The water evaporates leaving crystals of pure salt)
Simple distillation
-used to obtain a solvent from a solution
Fractional distillation
-separate mixtures in which the components have different boiling points
Chromatography
-separate the different soluble, coloured components of a mixture
The Periodic Table
Group 7
-
halogens
(non-metals)
-seven electrons in outer shell
reactivity decreases down group because outer shell gets further away from nucleus, so its less easy to gain an electron
-further down the group, the higher it relative molecular mass, m.p&b.p
-react with metals to produce ionic salts=halogen atom gains one electron to form a halide ion with a negative charge(-1)
-a more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt
Transition Metals
-centre of table between groups 2&3
-form coloured compounds
-have ions with different charges
-can be used with catalysts to speed up chemical reactions
-good conductors of heat/electricity, can easily be bent
Group 1
-
alkali metals
-one electron on outer shell
-low m.p&b.p- decrease down group
-become more reactive down the group
-outer electron gets further away from influence of nucleus, so lost more easily
-stored under oil- react with oxygen and water
-when reacted with water-metal hydroxide formed
-low density (lithium,sodium,potassium=less dense than water so they float)
-react with non-metals to form ionic compounds=metal atom loses one electron to form a metal ion with a positive charge(+1)
Group 0
-
noble gases
-full outer shell of electrons
-this=stable electron configuration, making them unreactive non-metals
-b.p increase down the group
The Development of the Periodic table
Dimitri Mendeleev(1869)
-when he created his table he left gaps to allow for their discovery. He also reordered some elements. Each element was placed in a vertical column or 'group' with elements that had similar properties. He used his table to predict existence and properties of new elements. When the subatomic particles were later discovered, it revealed that he organised them in order of increasing atomic number(no. of protons)
John Newlands(1864)
- only 63 elements known, he arranged the known elements in order of atomic weight. He noticed periodicity (repeated patterns), although the missing elements caused problems. Strictly following the order of atomic weight created issues- some elements were in the wrong place
Atoms and The Periodic Table
Subatomic particles