Chemistry Examples

S e

$S e$

Step 1

Find the element

Se

$Se$ on the periodic table.

34	Atomic Number
Se	Element Symbol
Selenium	Element Name
78.96	Average Atomic Mass

Step 2

The atomic weight is a measurement of the total number of particles in an atom's nucleus including both protons and neutrons. So the first step is to locate the atomic mass on the periodic table, and round the value to the nearest whole number.

78.96

$78.96$ round to

79

$79$

Step 3

The mass number is the number of particles in an atom's nucleus. The nucleus is made up of protons and neutrons.

Atomic Mass = Number of Protons + Number of Neutrons

$Atomic Mass = Number of Protons + Number of Neutrons$

Step 4

Find the element

Se

$Se$ on the periodic table.

34	Atomic Number
Se	Element Symbol
Selenium	Element Name
78.96	Average Atomic Mass

Step 5

To find the number of protons in

selenium

$selenium$ , first locate the element on the periodic table. Next, find the atomic number which is located above the element's symbol. Since

selenium

$selenium$ 's atomic number is

34

$34$ ,

Se

$Se$ has

34

$34$ protons.

34

$34$ protons

Step 6

Fill in the known values where

N

$N$ represents the number of neutrons.

79 = 34 + N

$79 = 34 + N$

Step 7

Rewrite the equation as

34 + N = 79

$34 + N = 79$ .

34 + N = 79

$34 + N = 79$

Step 8

Move all terms not containing

N

$N$ to the right side of the equation.

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Step 8.1

Subtract

34

$34$ from both sides of the equation.

N = 79 - 34

$N = 79 - 34$

Step 8.2

Subtract

34

$34$ from

79

$79$ .

N = 45

$N = 45$

N = 45

$N = 45$

S e

$S e$

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