Did you practice your conversions today?

1

2

Classifications of Matter

Pure Substances:Matter that has a fixed or definite composition

– Elements

• Composed of only one type of atom

– Compounds

• Composed of multiple types of atom

• Ex. Water (H2O)

• Always same proportion of hydrogen to oxygen

• Chemical process can break compounds down into simpler substances

3

4

Example: NaCl

5

Mixtures• Almost everything exists as a mixture (clean air,

water, etc.)

• Heterogeneous Mixture:– One or more visible boundaries; not uniform

– Example: milk

• Homogeneous Mixture:– No visible boundaries; individual atoms, ions or

molecules mixed

– Example: sugar water

Mixtures v. Compounds

In what ways are mixtures not compounds?

1. Proportions of the components can vary

2. The individual properties of the components are observable

3. The components can be separated by physical means

Pure substance or mixture?• Salt water

• Helium gas

• Vegetable soup

• Hydrogen peroxide (H2O2)

8

Are the mixtures homogeneous or heterogeneous?

MIXTURE

PURE / ELEMENT

MIXTURE

PURE / COMPOUND

Elements and Symbols• Elements:

– primary substances from which all other things are built.

– Cannot be broken down into simpler substances

• Chemical symbols– Each element has its own symbol

– One or two letter abbreviations

– First letter always capital letter

– Second letter always lowercase letter

– Ex. cobalt = Co

nitrogen = N9

Elements• Elements ordered by atomic number• “Periodic” trends• Periodic table by Mendeleev (1871)

1A 2A

3B 4B 5B 6B 7B 8B 1B 2B

3A 4A 5A 6A 7A

8A

Reading the Periodic TablePeriod: horizontal row Group: vertical column

Alkali Metals

soft, shiny metals; good electrical/thermal conductors

react vigorously with water

Alkaline earth metals:

shiny metals, less reactive than alkali metals

Halogens:strongly reactive (i.e. Cl2, Br2)

Noble Gases:

unreactive11

Metals, Nonmetals, and Metalloids

• Metals:– Left side of zigzag “staircase”

– Shiny solids (Hg is a liquid!)

– Ductile and malleable

– Good electrical/thermal conductors

• Nonmetals:– Dull

– Poor electrical/thermal conductors

– Lower melting points and densities

• Metalloids:– B, Si, Ge, As, Sb, Te, Po, At

12

The AtomAtom: smallest particle of an element that retains the

characteristics of that element.

Dalton’s Atomic Theory (1808) 1. All matter is made up of tiny particles called atoms

2. All atoms of a given element are:– Similar to one another

– Different from atoms of other elements

3. Compounds are combinations of atoms of two or more different elements. A particular compound always:– Is made up of same kinds of atoms

– Has the same number of each kind of atom

4. Chemical reaction: rearrangement, separation or combination of atoms 13

Structure of an Atom

Rutherford gold foil experiment

14

Atoms and Subatomic Particles

Diameter of one atom: 0.1 – 0.5 nm(Carbon atom: 0.15 nm)

15

Atomic Number and Mass Number

• Atomic Number

16

= # of protons in atom

• Atoms are electrically neutral• # protons = # electrons

• Mass Number

= # of protons + # of neutrons

IsotopesIsotopes: atoms of the same element that have

different numbers of neutrons

17

Mg

12

Atomic #

24

Mass #

Atomic Symbol

Isotopes of Carbon12C : 6 protons + 6 neutrons13C : 6 protons + 7 neutrons14C : 6 protons + 8 neutrons

18

98.89 %1.11 %

<0.01 %

All have nearly identical chemical behavior

Atomic Mass

• Atomic Mass: weighted average of masses of all the naturally occurring isotopes of that element

19

Example: chlorine

35Cl

37Cl

Mass (amu)

x Abundance (%)

Contribution to

average Cl atom

=

34.97

36.97

26.50 amu

8.954 amu

x

x

100

78.75

100

22.24

=

=

Atomic mass of Cl

+

35.45 amu

The Mole• 12 eggs = • 12 bagels = • 6.02 x 1023 hydrogen atoms =• 6.02 x 1023 water molecules =

20

1 dozen eggs

1 dozen bagels

1 mol H atoms

1 mol H2O

1 mole is a unit that contains 6.02 x 1023

(Avogadro’s Number)

How many water molecules are in 3.5 moles of water?

OH moles 3.5 2OH mole 1

molecules OH 10 6.02

2

223

2410 107.2

molecules OH 10 1.2 224

Electromagnetic Spectrum

Longer wavelength smaller energy

Shorter wavelength more energy

All waves in the EM spectrum travel at the same speed.

Speed of light: c = 3.00 x 108 m/s

Properties of Waves

22

Which wave has the longer wavelength?Which wave has more energy?

Carbon atoms

23

Atomic Spectra• When light passes through a prism, it is dispersed

– Splits into specific colors

• Each type of material will produce different wavelengths of light when heated.

• These patterns are called atomic spectra

Atomic Spectra

25

Energy States

Note: biggest “step” from n=1 to n=2

• Each atomic spectrum line is associated with an electronchanging energy

• Electrons can only have certain energy levels (quanta)

• Energy levels:• Principal quantum numbers• Positive integers• Smaller numbers

• closer to nucleus, lower energy • Bigger numbers

• Further from nucleus, higher energy

Changes in Energy Levels• Ground state: lowest level

– n = 1• Excited states: higher levels

– n = 2, 3, 4,…• Energy absorbed: electron

jumps up to higher E• Energy released: electron

drops down to lower E

If a photon is emitted, light may be observed. The color of the light emitted relates to the

wavelength of the photon emitted

Energy Sublevels

• Each level consists of sublevels• The number of sublevels in each level

equals the principal quantum number• n = 1 one sublevel• n = 2 two sublevels• n = 3 three sublevels• n = 4 four sublevels

28

1s2s & 2p3s & 3p & 3d4s & 4p & 4d & 4f

Increasing energy of sublevels within an energy level: s < p < d <

f

Orbitals

• There is no way to know exactly where an electron is in an atom

• Orbitals describe the regions with the highest probability of finding an electron

• Each type of orbital has a given shape:

29

s orbital

p orbitals

Orbitals

30

d orbitals

Each orbital can hold TWO electrons• s orbitals:

• p orbitals:

• d orbitals:

2 e-

6 e-10 e-

Orbital Energy Levels• Pauli Exclusion Principle:

– Any orbital can hold up to 2 electrons• Electrons want to sit in lowest energy level• Which is lower: 2s or 2p orbitals?• For a given n value:

– Order of sublevel energy: s < p < d < f

• Orbital Diagrams

1s

Orbital Diagram:

Electron Configurations• Periodic Table tells us the number of e- in an atom

32

Electron Configuration:

tells us which orbitals electrons are in for a given atom

Example: Hydrogen Atomic Number:

1

(How many electrons?)

1

Electron Configuration:

1s

1

1s

Orbital Diagram:

Electron Configurations

33

Example: Helium Atomic Number:

2

(How many electrons?)

2

Electron Configuration:

1s

2

1s

Orbital Diagram:

Example: Lithium Atomic Number:

3

(How many electrons?)

3

Electron Configuration:

1s

2

2s

2s

1

1s

Orbital Diagram:

Electron Configurations

34

Example: Boron Atomic Number:

5

(How many electrons?)

5

Electron Configuration:

1s

2

2s

2p

2s

22p1

1s

Orbital Diagram:

Electron Configurations

35

Example: Oxygen Atomic Number:

8

(How many electrons?)

8

Electron Configuration:

1s

2

2s

2p

2s

2 2p4

Abbreviated Configuration:

[He]

2s

2 42p

Electron Configurations relate to the Periodic Table!

• For s block elements: electron configuration should end with electrons in s orbitals– Ex. Na: 1s2 2s2 2p6 3s1

• For p block elements: electron configurations should end with electrons in p orbitals– Ex. P: 1s2 2s2 2p6 3s2 3p3

• For d block elements: electron configurations should end with electrons in d orbitals– Ex. Ni: 1s2 2s2 2p6 3s2 3p6 4s2 3d8

Note: 4s orbital comes before 3d orbital

Sublevel Order

Exceptions in sublevel order: Cr: 1s2 2s2 2p6 3s2 3p6 4s2 3d4

Cr: 1s2 2s2 2p6 3s2 3p6 4s1 3d5

Cu: 1s2 2s2 2p6 3s2 3p6 4s2 3d9

Cu: 1s2 2s2 2p6 3s2 3p6 4s1 3d10

Half-filled or totally filled orbitals are more stable

Periodic TrendsValence electrons:

– Outermost electrons (last e- in electron config.)– Responsible for chemical behavior– Elements in a group have same number of valence e-

– Elements in a group have similar chemical properties

38

Electron-Dot Symbols

Boron (B): 1s2 2s2

2p1 How many valence

electrons?3

B

Periodic Trends

39

Electron-Dot Symbols

Alumnium (Al):

How many valence electrons?

3 Al

1s2 2s2 2p6 3s2

3p1

Chlorine(Cl):

How many valence electrons?

7 Cl

1s2 2s2 2p6 3s2

3p5

Periodic Trend: Atomic Size

40

(stronger pull from nucleus)

(more energy levels)

Atomic radius: distance from nucleus to outermost e-

• Decreases across a period

• Increases down a group

Ionization: removing an e- from an atom

Increases across a period

Decreases down a group

Periodic Trend: Ionization Energy

41

(stronger pull from nucleus)

(further from nucleus)

A neutral atom has 7 protons and 7 neutrons:-What is the mass number? -How many electrons does this element have?-What is the atomic number? -What Element is this?-Is the atomic size Larger or Smaller than Boron? -Is the atomic size Larger or Smaller than Phosphorus?-What is the electron configuration? -How many valence electrons? -Write the electron dot symbol for this atom

3

7

7

Nitrogen

Smaller

Smaller

1s2 2s2 2p3

14

N.. ..

.