Atomic ParticlesProton

p+

Neutronn

Electrone-

Mass /kg 1.672x10-27 1.674x10-27 9.109x10-31

Charge/C 1.602x10-19 0 1.602x10-19

Relative mass

1 1 1/1800negligible

Relative charge

+1 0 -1

Atomic Structure

Important NumbersMass number (A) is the total number of protons + neutrons in the nucleus

23

Na 11

• Atomic number (Z) is the number of protons in the nucleus

Numbers of particles• No. of p+ = Atomic Number (Z)

• No. of e- = No. of p+ (atom is uncharged)

• No. of n = Mass Number – Atomic Number (A) (Z)

• No. of n = No. of p + + n – No. of p +

23

Na 11

• 11 p+ (Atomic number Z)• 11 e- (No. p+ = No. e-)• 12 n (mass number – atomic number)

A – Z 23 – 11 = 12

Numbers of particles

Isotopes8 neutrons (14-6 = 8)6 neutrons

(12-6 = 6)

6 protons6 protonsIsotopes are atoms of the same

element with the same atomic number but different mass numbers

• Isotopes of an element have the same chemical properties because they have the same Atomic Number, Z (same no. p+ & e-)

• Isotopes have different Mass Number, A, so they have slightly different physical properties– Masses - more/less neutrons– Melting & boiling points – forces of attraction different strengths– Densities – atoms are the same size but different mass– Rate of diffusion

Isotopes

Uses of Isotopes• Some isotopes are radioactive

• Iodine-131 injected into bloodstream to detect tumors

• Iron-59 used to monitor redblood cell production in bone marrow

• Sodium-24 used to detect blood clots

• Ratio of carbon-12 to carbon-14 used to date objects – Carbon dating