Atomic Structure 5j6b41

Chapter 4 Atomic Structure

Defining the Atom  All elements are composed of particles called atoms  All atoms of the same element are identical  Atoms of different elements combine to form compounds  Atoms of one element can never be changed into another element

History of the Atom  Democritus (Greek 460-370 BC) • 1st to use the word atom • Believed that atoms were indivisible & indestructible • No scientific

 Aristotle (Greek 384-322 BC) • Rejected the theory of atoms • Believed in 4 core elements fire, air, water, earth

 Antoine Lavoisier (French 1743-1794) • Law of Conservation of Matter – Matter is not created or destroyed during a chemical reaction

 Joseph Proust (French 1754-1826) • Law of Definite Proportions A compound is always composed of the same elements, in the same proportion by mass

 John Dalton (English 1766-1844) • Studied the ratio in which elements combine • Quantitative data – mass • Law of Multiple Proportions When 2 elements form more than one compound, they do so in a ratio of whole numbers

Dalton’s Atomic Theory 1. All elements are composed of indivisible ‘solid sphere’ atoms. 2. All atoms of a given element are identical. 3. Atoms of different elements differ in their masses. 4. Different atoms combine in simple whole number ratios to form compounds.

Structure of the Atom

Subatomic Particles  Today… Dalton’s Atomic Theory has one important change  Atoms are divisible…  3 types of subatomic particles • Protons • Neutrons • Electrons

Electrons  J.J. Thomson (English 1897) – • Identified the 1st subatomic particle • Cathode-ray tube

Thomson’s Electron Model Named electrons Symbol: eCharge: (-1) Mass: ~ 0 amu Plum Pudding/ Chocolate Chip Cookie     

What about the protons & neutrons?  Protons • Symbol: p+ • Charge: (+1) • Mass: 1 amu  Neutons • Symbol: n0 • Charge: (0) neutral • Mass: 1 amu

The Nucleus  Ernest Rutherford (English 1911) • Discovered the ‘structure’ of the atom • Gold foil experiment Rutherford’s Gold Foil Experiment

Rutherford’s Nuclear Model Atom is mostly empty space Atoms have a dense center – nucleus Most of the mass is in the nucleus Nucleus has a positive charge Protons & neutrons are located in the nucleus  Electrons are outside of the nucleus & occupy most of the atom’s volume     

Distinguishing Among Atoms

What makes atoms different from one another?   

# of protons Atomic number = # of protons Usually written as a subscript Mg12 or 12Mg

What element has 11 protons? Sodium How many protons does potassium have? 19

How do you determine the # of neutrons?  Atomic mass = # protons + # neutrons  Usually written as a superscript 12C or C12 or C -12  # of neutrons is the difference between the atomic mass & the atomic number # of neutrons = atomic mass - atomic #

What is the atomic mass of helium? 4.0026… round to 4 What element has an atomic mass of 27? Aluminum How many protons does this element contain? 13 How many neutrons does this element contain? 27 – 13 = 14

What about electrons?  # electrons = # of protons  Why? • Atoms are electrically neutral How many electrons does sulfur contain? 16 Which element contains 10 electrons? Neon

Sample Problems  How many protons, neutrons and electrons are in each atom? Beryllium (Be) -

4, 5, 4

Fluorine (F) -

9, 10, 9

Hydrogen (H) -

1, 0, 1

 How many neutrons are in each atom? O16

8

108 47Ag

Pb207

82

16 – 8 = 8

108 – 47 = 61

207 – 82 = 125

 Express the composition of each atom in shorthand form. Nitrogen -14

p+ = 7, n0 = 7, e- = 7

Sodium - 23

p+ = 11, n0 = 12, e- = 11

Phosphorus -31 p+ = 15 , n0 = 16, e- = 15

Isotopes  Atoms that contain the same number of protons but have different numbers of neutrons  Different atomic masses  Does not change the atom’s identity  Are naturally occurring  Symbols: Na23 or

11

Na24

11

C12 or 6C13 or

6

C14

6

 Determine the number of protons, neutrons and electrons in the following: H1

p+ = 1, n0 = 0, e- = 1

H

p+ = 1, n0 = 1, e- = 1

1

1

2

H3

1

p+ = 1, n0 = 2, e- = 1

Determining the Atomic Mass  Atomic mass # is an average of atom’s naturally occurring isotopes Copper has 2 isotopes Cu-63 and Cu-65 Which isotope is most abundant? 63 There are 3 isotopes of Silicon with mass numbers of 28, 29, and 30. Si -28 Which is more abundant?

Calculating the Atomic Mass  Multiply the mass of each isotope by its natural abundance (expressed as a decimal), then add the products  Practice…

Ions  An atom with an electrical charge  Occurs 2 ways: • Oxidation – loss of an eresults in a (+) charge • Reduction – gain of an eresults in a (-) charge Mnemonic: ‘Leo says Ger’ Loss of electrons = oxidation Gain of electrons = reduction

Examples of Ions    

H+ ClAs3Mg2+

Lost 1eGained 1eGained 3eLost 2e-

 Oxidation State – • Number found on the periodic table • Shows the number of e- gained or lost • Many elements have more than one number