Atom is the smallest particle of an element.
| An image of an atom |
Recap:
Atoms consists of 3 main parts
1. The neutrons
- Has a neutral charge
- Is found in the nucleus
2. The protons
- Has a positive charge
- Is also found in the nucleus
- Has a negative charge
- Is found in electrons shells that orbits around the nucleus in a fixed path
Proton/ Atomic number and Mass/ Neucleon number
The Proton/ Atomic number refers to the number of protons or electrons in an atom since there is a equal number of protons and electrons in an atom. While the Mass/ Neucleon number refers to the sum of protons/ electrons and neutrons.The Proton/ Atomic number and Mass/ Nucleon number of an element is found beside the chemical symbol of the element in the periodic table.
Arrangement of Electrons in Atoms
The arrangement of electrons in atoms, known as electronic structure or electronic configuration, are very important because the arrangement affects the chemical properties of an atom.Electrons are found in electron shells, each electron shell can only hold a certain number of electrons.
Rules of the arrangment of electrons in an atom:
- 1st shell: Strictly only a maximum2 electrons
- 2nd and 3rd shell: Strictly only a maximum 8 electrons in each shell
- Each shell must be completely fill with the maximum number of electrons before the next shell can be filled up.
Ions
Definition of an ion:
A charged particle at created from an atom of a group of atoms by the loss or gain of electrons.
- 1st scenario: When an atom gains electrons (but the number of neutrons and protons remain the same), the atom becomes a negative ion with a negative charge.
- 2nd scenario: When an atom loses electrons (but the number of neutrons and protons remain the same), the atom becomes a positive ion with a positive charge.
Why do atoms become ions?
The loss or gain of electrons is due to its chemical unstability. In order to acheive chemical stability, the atom must have a noble gas structure, which means each electron shell of the atom have to be fully filled with electrons.
However, there are still atoms that are originally chemically stable, in other words, the are already in the noble gas structure. Thus, they are very unlikely to become ions (to stay in the monatomic state) unless being forced.
- These atoms of elements are found at group "0" of the periodic table. E.g. Helium, Argon, etc.
- These atoms have a unreactive or chemically configuration, which we also call the noble gas configuration or noble gas structure.
How do the electrons of an atom know what to do (i.e.where to go) so as to acheive the noble gas structure?
- 1st scenario: Metals - Atoms of metal tend to lose electrons and form positiely-charged ions, also known as Cations (read as cat-ions).
- 2nd scenario: Non-metals - Atoms of non-metals tend to gain electrons and form negatively-charged ions, also known as anions (read as an-ions).
Molecules
Definition of molecules:
Molecules are atoms that share electrons with another atom(s). Molecules are made up of at least 2 or more atoms chemically combined together.
Molecules of elements
- Molecules of elements usually consist of a fixed/ constant number of one type of atom combined chemically.
- Many non-metals tend to exist as molecules.
- Molecules that consists of only 2 atoms are called diatomic molecules. (These elements of atoms can be found under group VII of the periodic table).
Molecules of compounds
- Molecules of compounds are formed when fixed number of different types of atoms are chemically combined.
- The number of different types of atoms are always constant.
Chemical formula
Each chemical formula represents a particular substance. A compound is represented by a chemical formula which from the formula we can infer the types of atoms present in the compound and the ratio of the different atoms present in the atom. On the other hand, scientists communicate with each another by their comman known language - chemical symbols and formulae.
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