GCSE - Atoms and the Periodic Table

Information about Atoms and the Periodic Table for GCSE C2/3

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Atoms Part 1

An atom is the basic unit of a chemical element.

There are 2 layers of atom: (from inside out) The nucleus - made of protons and neutrons and the electrons which "fly around" the nucleus at extreme speeds.But the electrons are NOT moving around the nucleus along the circles.

(http://www.chemguide.co.uk/atoms/properties/nastruct2.gif)

Instead, the circles represent energy levels. The electrons in the shell closest to the nucleus have the lowest energy. A shell is a layer of electrons.

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Atoms Part 2

  • The number of protons in an atom is called its atomic number.
  • In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
  • All atoms of a particular element have the same number of protons.
  • Atoms of different elements have different numbers of protons.

The relative electrical charges are

  • Proton - Mass 1, electrical charge +1
  • Electron - Mass almost 0, electrical charge -1
  • Neutrons - Mass 1, electrical charge 0

Atoms have no overall charge and are neutral. This means there is the same number of positive protons and negative electrons.

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Atoms Part 3

Electrons have a mass of almost zero, which means that the mass of each atom results almost entirely from the number of protons and neutrons in the nucleus.  

The sum of the protons and neutrons in an atom’s nucleus is the mass number. It is the larger of the two numbers shown in most periodic tables.

Atomic number is the number of protons rather than the number of electrons, because atoms can lose or gain electrons but do not normally lose or gain protons.

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The Periodic Table

  • The Periodic Table lists all of the elements, which are substances which can't be simplified in separation. The are the building blocks of the universe.
  • The elements in Group 1 of the periodic table,(alkali metals) have similar chemical properties. They all react with non-metal elements and make ionic compounds in which the metal ion has a single positive charge.
  • The elements in Group 7 of the periodic table, (halogens) have similar chemical properties. They react with the alkali metals to form ionic compounds in which the halide ions have a single negative charge
  • In the periodic table between Groups 2 and 3 is a block of elements known as the transition elements. These elements are all metals.
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The Periodic Table

(http://chemed.chem.wisc.edu/~tsts/Stahl/Stahl%209-12%20Images/PeriodicTable.jpg)

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History of the Periodic Table

In 1864, when around 50 elements were known, a British chemist called John Newlands saw a pattern between them. He saw that in the elements the properties repeated every 8th element. He called it the Law of Octaves, as he was comparing it to musical notes.

However, it was only correct up to Calcium. He placed highly reactive lithium, sodium and potassium in the same group as copper, which is unreactive.

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The Periodic Table

An element is a substance which is only made from one type of atom.

There are 92 natural elements, and about 15 artificial ones.

Elements were origianally made in a star's early life, when light elements like hydrogen and helium are made, then fused together to form heavier ones like carbon.

Most of the artificial ones are made in nuclear reactors or particle accelerators

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History of the Periodic Table

Mandeleev was a Russian scientist who realised all of the patterns of elements. He created the modern periodic table in 1869.

He found that the properties of all elements had a relation to atomic mass in a "periodic way". He made the table so that the groups with similar properties were in vertical columns.

Because of this way of arranging, there were gaps in the table, but Mandeleev just assumed this was because these elements hadn't been discovered yet. And he was right!

He used Newlands theory as a base, but Mandeleev's was backed up from the new discoveries made which fit in to the gaps.

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Periodic Table

 

 

The columns ( | )in the table are called Groups

The rows ( -- ) are called Periods.

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