Atoms, Ions and Isotopes

Subatomic Particles Particle Symbol Charge Relative Mass (amu) Electron e- 1- 0 Proton p+ 1+ 1 Neutron n 0 1

Atomic Number the number of protons in an atom All atoms of the same element have the same number of protons Atomic Number

Number of Electrons If an atom is neutral, the net charge is zero Number of protons = Number of electrons

Mass Number Mass Number = protons + neutrons number of neutrons = mass number – atomic number *Mass number is NOT on the periodic table

Atomic Symbols atomic number 11 Show the mass number and atomic number Give the symbol of the element mass number 23 Na or Sodium-23 (Na-23) atomic number 11

More Atomic Symbols 16 31 65 8 15 30 O P Zn 8 p+ 15 p+ 30 p+ 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n (16-8) 16 n (31-15) 35 n (65-30) 8 e- 15 e- 30 e-

Isotopes Atoms with the same number of protons, but different numbers of neutrons. Same atomic number Different mass numbers Isotopes of chlorine 35Cl 37Cl 17 17 chlorine - 35 chlorine – 37 Cl – 35 Cl - 35

Ions An atom that has gained or lost electrons An atom that loses electrons has a positive charge (+) Positive ions are called cations ex. Na+, Mg+2 An atoms that gains electrons has a negative charge Negative ions are called anions Ex. Cl-, O-2 How many protons, neutrons, and electrons are there in the Calcium ion (Ca+2)? How many protons, neutrons, and electrons are there in the Fluoride ion (F -)?

Learning Check AT 5 16 14 14 An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14

Masses of Atoms A scale designed for atoms gives their small atomic masses in atomic mass units (amu) An atom of 12C was assigned an exact mass of 12.00 amu Relative masses of all other atoms was determined by comparing each to the mass of 12C

Calculating Average Atomic Mass You need to know… Percent(%) abundance of isotopes Mass of each isotope Weighted average = (mass of isotope 1)(% abundance/100) +(mass of isotope 2)(% abundance/100) + …

Atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70% 25Mg = 25.0 amu 10.13% 26Mg = 26.0 amu 11.17% (.7870 x 24.0) + (.1013 x 25.0) + (.1117 x 26.0) Atomic mass (average mass) Mg = 24.3 amu Mg 24.3

Learning Check AT7 Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the average atomic mass of gallium?

Solution AT7 Atomic mass Ga = 69.7 amu 68.9 amu x 60.2 = 41.5 amu for 69Ga 100 Ga-71 (%/100) 70.9 amu x 39.8 = 28.2 amu for 71Ga Atomic mass Ga = 69.7 amu