Question

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

1)

Atomic number of Se = 34

So, number of proton = 34

use:

charge = number of proton - number of electron

-2 = 34 - number of electron

number of electron = 36

number of neutron = mass number - atomic number

= 78 - 34

= 44

44

34

36

2)

number of proton = mass number - number of neutron

= 65 - 36

= 29

29 is atomic number for Cu

use:

charge = number of proton - number of electron

+1 = 29 - number of electron

number of electron = 28

Cu

29

28

3)

Atomic number is 36 for Kr

use:

charge = number of proton - number of electron

= 36 - 36

= 0

use:

mass number = number of proton + number of neutron

= 36 + 42

= 78

Kr

78

0