The atomic number is the number of protons in an atom.

The mass number is the sum of protons & neutrons in an atom.

Atomic number (written at the left side below the symbol is 8) = 8 protons.

Mass number (written at the left side above the symbol is 16)

No. of neutrons = 16 – 8 = 8

Nitrogen

Atomic number = no. of protons = 7

Mass number = protons + neutrons = 14

Number of neutrons = 14 - 7 = 7

Complete the following table:

Element symbol	Atomic number	Mass number	Number of protons	Number of neutrons

An atom is electrically neutral because the number of protons = the number of electrons. The positive charge of the proton is opposite to that of the electrons.

Electrons revolve around the nucleus in orbits called energy levels.

a. Energy levels are places around the nucleus where electrons exist.

b. There are 7 energy levels represented from the nearest to the nucleus to the farthest by the letters K, L, M, N, O, P, Q.

c. The energy of the level increases by the increase of the distance from the nucleus.

d. Each level is saturated (completely filled) with a certain number of electrons.

e. The number of electros which saturate energy levels 1-4 is calculated by the rule 2n²

Where n is the number of the energy level.

No. of energy level	It symbol	The number of electrons that saturate the levels
	K	2 (1)^2 = 2
	L	2 (2)^2 = 8
	M	2 (3)^2 = 18
	N	2 (4)^2 = 32
	O	32 electrons. The equation isn’t applied because a number of electrons larger than 32 makes the atom unstable.
	P
	Q

f. When an electron gains a quantum of energy, it moves to a higher energy level. The atom is excited by gaining energy.

g. The excited atom loses the quantum of energy & electrons return to the original level (ground state)

Distributing electrons in energy levels electronic configuration.

Mass number symbol atomic	Electronic configuration
	K
	K
	L K
	L K

Complete the following table:

Symbol

Mass number Atomic number	Electronic configuration

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Дата добавления: 2015-10-28