Atomic number and mass number
Atomic number
The The number of protons in the nucleus of an atom. Also called the proton number. of an The smallest part of an element that can exist.is the number of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. in its The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei.. Remember that:
- all the atoms of a given A substance made of one type of atom only. have the same atomic number
- the atomic number of each element is unique - no two elements have the same atomic number
An atom contains an equal number of protons and Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. Since protons and electrons have equal and opposite An imbalance of electrons and protons in a material. An excess of electrons results in negative charge, a deficit of electrons results in positive charge., this means that atoms are An atom in which the number of protons and electrons is the same. overall.
For example, the atomic number of lithium is 3. Every lithium atom has 3 protons and 3 electrons. It has 3 positive charges and 3 negative charges.
Mass number
Atoms of different elements usually have different The number of protons and neutrons found in the nucleus of an atom., but they can be the same. For example, the mass number of argon atoms and calcium atoms can both be 40.
Calculating numbers of subatomic particles
The symbol for an atom can be written to show its mass number and its atomic number.
To calculate the numbers of Objects found in atoms, including protons, neutrons and electrons. in an atom use its atomic number and mass number:
- number of protons = atomic number
- number of electrons = atomic number
- number of Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. = mass number - atomic number
Example
The atomic number of a fluorine atom is 9 and its mass number is 19. Calculate the number of protons, neutrons and electrons it contains.
number of protons = 9
number of electrons = 9
number of neutrons = mass number - atomic number
= 19 - 9 = 10