the atom


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1. Formulae, equations and amounts of substance
Nuclei of atoms are made up of protons and neutrons
The electrons in the atom occupy the space outside the nucleus
Protons have a positive charge
Electrons have a negative charge
Neutrons have no charge
An element is a substance that cannot be broken down chemically into simpler
Atoms of an element all contain the same number of protons
The number of protons in the nucleus is the atomic number (given the letter Z in
The number of protons is equal to the number of electrons, an atom is
electrically neutral
The number of protons (Z) plus the number of neutrons (N) in an atom is known
as the mass number (A)
Atoms with the same atomic number but different numbers of neutrons are
called isotopes
Most elements are a mixture of isotopes
Different isotopes of the same elements may have different physical properties,
they have a different mass and some may be radioactive, these always have the
same chemical properties because the number of electrons stays the same
Holding atoms together
In compounds formed between metals and nonmetals, the atoms are usually
joined by ionic bonding
An atom that loses or gains one or more electrons forms an ion
An atom that loses an electron becomes a positive ion
An atom that gains an electron becomes a negative ion

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Many chemical reactions do not involve ions
Nonmetals generally gain electrons to achieve a stable outer shell
When nonmetals react together, the atoms achieve full outer shells by sharing
electrons covalent bonding
Strong bonds between atoms=covalent bonds…read more


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