Chem
- Created by: toniocourtaio
- Created on: 30-09-15 22:21
View mindmap
- Chemistry
- Structure of the atom
- The nuclear model
- The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in shells around the nucleus.
- Atoms contain three sub-atomic particles called protons, neutrons and electrons.
- Properties of sub-atomic particles
- The number of electrons in an atom is always the same as the number of protons, so atoms are electrically neutral overall.
- The nuclear model
- Isotopes
- Atomic number and mass number
- The proton number is shown below the chemical symbol, and the mass number is shown above. In chlorine the atomic number is 17 and the mass number is 35.
- Isotopes are atoms of an element with the normal number of protons and electrons, but different numbers of neutrons. Isotopes have the same atomic number, but different mass numbers.
- Atomic number and mass number
- Relative atomic mass
- Different atoms have different masses. Atoms have such a small mass it is more convenient to know their masses compared to each other. Carbon is taken as the standard atom and has a relative atomic mass (Ar) of 12.
- Ar values of elements
- These values tell you that a magnesium atom has twice the mass of a carbon atom, and 24 times more mass than a hydrogen atom. They also tell you that hydrogen atoms have 12 times less mass than a carbon atom. The Ar values also allow you to work out that three oxygen atoms have the same mass as two magnesium atoms.
- The relative atomic mass of an element is a weighted average of the masses of the atoms of the isotopes - because if there is much more of one isotope then that will influence the average mass much more than the less abundant isotope will.
- Formation of ionic compounds
- When metals react with non-metals, electrons are transferred from the metal atoms to the non-metal atoms, forming ions. The resulting compound is called an ionic compound.
- In all of these reactions, the metal atoms give electrons to the non-metal atoms. The metal atoms become positive ions and the non-metal atoms become negative ions.
- Structure of the atom
Comments
No comments have yet been made