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)

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.