Classifications of Matter - General Chemistry - Lecture Slides, Slides for Chemistry. B R Ambedkar National Institute of Technology
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Classifications of Matter - General Chemistry - Lecture Slides, Slides for Chemistry. B R Ambedkar National Institute of Technology

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General Chemistry course covers the fundamentals of chemistry which includes: structure of atom/molecules, thermodynamics, stoichiometry, equilibrium and acid base chemistry. Keywords from these slides are: Classificatio...
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Slide 1

1

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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

2

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3

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Example: NaCl

4

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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

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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

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Pure substance or mixture?

• Salt water

• Helium gas

• Vegetable soup

• Hydrogen peroxide (H2O2)

7

Are the mixtures homogeneous or heterogeneous?

MIXTURE

PURE / ELEMENT

MIXTURE

PURE / COMPOUND

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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 = N 8

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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

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Reading the Periodic Table

Period: 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:

unreactive 10

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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

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The Atom Atom: 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 12 docsity.com

Structure of an Atom Rutherford gold foil experiment

13

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Atoms and Subatomic Particles

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

14

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Atomic Number and Mass Number

• Atomic Number

15

= # of protons in atom

• Atoms are electrically neutral

• # protons = # electrons

• Mass Number = # of protons + # of neutrons

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Isotopes Isotopes:

atoms of the same element that have different numbers of neutrons

16

Mg 12

Atomic #

24 Mass #

Atomic Symbol

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Isotopes of Carbon

12C : 6 protons + 6 neutrons 13C : 6 protons + 7 neutrons 14C : 6 protons + 8 neutrons

17

98.89 %

1.11 %

<0.01 %

All have nearly identical chemical behavior

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Atomic Mass

• Atomic Mass: weighted average of masses of all

the naturally occurring isotopes of that element

18

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

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The Mole

• 12 eggs =

• 12 bagels =

• 6.02 x 1023 hydrogen atoms =

• 6.02 x 1023 water molecules =

19

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 2 OH mole 1

molecules OH 10 6.02

2

2

23  2410 107.2 

molecules OH 10 1.2 2 24

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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

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Properties of Waves

21

Which wave has the longer wavelength?

Which wave has more energy?

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Carbon atoms

22

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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

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Atomic Spectra

24

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Energy States

Note: biggest “step”

from n=1 to n=2

• Each atomic spectrum line is

associated with an electron

changing 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 docsity.com

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