Identify the missing information for each atom or ion. Note that the atoms and ions are not necessarily neutral.
A Se ion has a mass number of 78 and a charge of −2 . Determine the number of neutrons, protons, and electrons in this ion.

number of neutrons:

number of protons:

number of electrons:

An ion has a mass number of 65, 36 neutrons, and a charge of +1 . Identify the element symbol, and determine the number of protons and electrons in this ion.

element symbol:

number of protons:

number of electrons:

An atom or ion has 42 neutrons , 36 protons, and 36 electrons. Identify the element symbol, and determine the mass number and charge for this atom or ion.

element symbol:

mass number:

charge:

Answer :

(1) Number of neutrons:  44

Number of protons:  34

Number of electrons: 36

(2) Element symbol:  Ni

Number of protons:  29

Number of electrons: 28

(3) Element symbol:  Kr

Mass number:  78

Charge: 0

Explanation :

Atomic number : It is defined as the number of protons or number of electrons.

Atomic number = number of protons

Mass number : It is defined as the sum of number of protons and number of neutrons.

Number of neutrons = Mass number - Atomic number

Part 1:

Element = Se (selenium)

Mass number = 78

Atomic number = 34

Charge on Se = -2

Atomic number = Number of protons = 34

Number of electrons = Number of protons - charge = 34 - (-2) = 36

Number of neutrons = Mass number - Atomic number = 78 - 34 = 44

Part 2:

Mass number = 65

Number of neutrons = 36

Charge on Se = +1

Number of neutrons = Mass number - Atomic number

36 = 65 - Atomic number

Atomic number = 65 - 36 = 29

Atomic number = Number of protons = 29

Number of electrons = Number of protons - charge = 29 - (+1) = 28

The symbol of element is, Nickel (Ni)

Part 3:

Number of neutrons = 42

Number of protons = 36

Number of electrons = 36

Atomic number = Number of protons = 36

Number of neutrons = Mass number - Atomic number

42 = Mass number - 36

Mass number = 42 + 36 = 78

Number of electrons = Number of protons - charge

36 = 36 - charge

Charge = 0

The symbol of element is, Krypton (Kr)

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