What is chemistry? “Chemistry is the study of the composition, structure, and the properties of...

What is chemistry?

• “Chemistry is the study of the composition, structure, and the properties of matter and the changes it undergoes.” from Modern Chemistry

• All chemical reactions involve energy.

Chemistry – Matter Unit

• What is matter?• What is

chemistry?• What is the

organization of matter?

• What is the nature of matter?

Is Air matter?

• What are the two criteria for matter?–Does it take up

space?–Does it have

mass?

What is the composition of matter?

Matter

Pure Matter Substance

Impure Matter Mixture

What is a pure substance?

• A pure substance has a definite composition (proportion).

• The composition of a substance will have the same percent of elements no matter where the sample was obtained. – Water from the White River and water from

the Pacific Ocean (once cleaned up) will have the same composition of hydrogen to oxygen.

– Gold is the same as other gold (once cleaned up).

What is a pure substance?

• A pure substance, by definition, is an element or a compound.

• A container with an almost pure compound:

Pure Substance

Pure Substance

Element Compound

What is an element?

• “a pure substance made of only one kind of atom” from Modern Chemistry

• A substance that cannot be decomposed any farther by simple chemical means

• An element has a definite composition. Gold from South Africa is the same, when purified, as a sample from California.

Periodic Table of Elements

• Most elements on the periodic chart are metals.• Elements through 114 but not 113 have been discovered

or made.

Elemental Samples

• Zinc, copper, lead, carbon, sulphur

What is a compound?

• “A compound is a substance that is made from the atoms of two or more elements that are chemically bonded.” From Modern Chemistry

• The definition is actually more involved than this.

What is a compound?

• A compound is a substance that cannot be decomposed any farther by simple physical means.

• A compound has a definite composition by mass.

• A compound is made up of two or more elements chemically combined.

What is a compound?

• A compound no longer has the properties of its constituent elements.

• Table salt, NaCl or sodium chloride, is a compound of the element sodium and the element chlorine.

Sodium

Sodium metal

• Soft, can be cut with a knife

• Shiny• Good

conductor of electricity

• Very reactive

Sodium in water

Chlorine gas

Chlorine gas

• Greenish gas

• Poisonous

• Heavier than air

Sodium in chlorine gas

Sodium chloride, NaCl

• Sodium chloride dissolves in water rather than reacts with water.

• Sodium chloride is a white solid, not a poisonous green gas.

• Sodium chloride is its own substance with its own properties, not those of either sodium or chlorine.

Samples of Other Compounds

• Sucrose (table sugar), Sodium Chloride, Water, Copper(II) sulfate

Coloured Compounds

• Cobalt(II) chloride, Iron(II) sulfate, Potassium dichromate, Potassium chromate, Nickel(II)

nitrate, copper(II) sulfate

What is the composition of matter?

Matter

Pure Substance Impure Matter

Mixture

Impure Matter - Mixture

• “A mixture is a blend of two or more kinds of matter, each of which retains its own identity and properties.” from Modern Chemistry

• A mixture is made up of two or more substances that are not chemically combined.

Mixtures• Mixtures can be separated by simple

physical means.• Two mixtures containing the same

substances may not have the same proportions.

• Example: Very salty water versus barely salty water. Very sweet sugar water versus slightly sweet sugar water.

Water and Dye Mixture

• Two mixtures of the same substances may have different proportions.

Mixtures

Mixtures

Homogeneous Mixture

Heterogeneous Mixture

?

Homogeneous Mixture• Homogeneous mixtures are uniform in

composition.• They have the same proportion of

components throughout.• Homogeneous mixtures are called

solutions.• Salt water is an example.• Solute + solvent = solution

H. W

• Examples of solutions

• g-g

• g-l

• s-s


• Heterogeneous mixtures are not uniform throughout.

• Clay particles in water are an example.

• Starch in water

Heterogeneous Mixtures

• Sand and water on the left and sand and gravel on the right.

Particle Size

• The particle size for homogeneous and heterogeneous mixtures is defined.– The solute particles for homogeneous

mixtures are so small that they cannot be seen.

– Heterogeneous mixture particles are visible.

Particle Size

• If the particles are spread evenly throughout the mixture but are not quite but almost visible, a colloidal suspension exists.

• An actual particle size is defined to differentiate among homogeneous mixtures, heterogeneous mixtures, and colloidal suspensions.

Colloidal Suspension

• Fog

Tyndall Effect

Examples of solutions and colloids

Categories Solutions Colloids

Solid in liquid Salt water

Sugar water

Gelatin (jello), paint, clays

Solid in gas Smoke

Solid in solid Alloys (steel, bronze, brass)

Black diamond


Examples Solutions Colloids

Liquid in liquid

Alcohol in water Milk (emulsion), mayonnaise

Liquid in gas Fog (aerosol),

Liquid in solid Mercury in silver and tin

Butter, cheese


Categories Solutions Colloids

Gas in gas Air

Gas in liquid Carbonated water

Whipped cream (foam)

Gas in solid Marshmallow, polystyrene foam

Mixtures vs. Compounds

• Rocks are mixtures.

• Minerals are pure substances

• Granite rock

Mixtures vs Compounds

• Minerals are pure substances although many have impuities that must be cleaned up first.

Minerals

Amethyst

Halite

Diamond

What is the nature of matter?

• An atom is the smallest unit of an element that maintains the properties of that element. From Modern Chemistry– An atom is made up of electrons,

protons, and neutrons as well as other particles.• Protons and neutrons are made up of

quarks.

What is the nature of matter?

• A molecule is a unit that consists of more than one atom bonded together.

• A molecule can have atoms of the same element such as oxygen. These are called diatomic elements.

2O

Blue – diatomic elements

Diatomic elements – blue

Tetraatomic element – red

Octatomic element - yellow

What is the nature of mature?

• A molecule can have atoms of more than one type of element.

• Water

• Sugar (sucrose)

OH2

112212 OHC

Atoms and Molecules

• Three particles:– 2 atoms of

hydrogen– 1 atom of

oxygen

• One particle:– 1 molecule of

water

Atoms• How can an atom of an element be

broken up into atoms of other elements or into other smaller particles and energy?

•Nuclear Reaction

Compound• How is a compound broken up into its

elements or other simpler compounds?

–Use a chemical separation method.

• What are some examples of chemical separation methods?

Chemical Separation Methods

• Heat the compound.

Chemical Separation Methods

• Use Electrolysis which is using an electric current to decompose the compound.

• An electrolyte has been added to the water since water does not conduct.

Mixtures

• How can mixtures be separated?

–Use Physical Separation Methods.

What are examples of physical separation methods?

Physical Separation Methods

• Distillation is the separation of mixtures by using the difference in boiling points of liquids.

• A water cooled condenser is used.


• Filtration uses the difference in particle size to separate mixtures.

• Filter papers have different size pores.


• Chromatography uses the difference in solubility in various solvents.

• Gas, liquid, thin layer, and paper chromatography are widely used.

States of Matter

• Three states of matter:

• Liquid, solid, gas

Physical Changes

• During physical changes matter changes in appearance without forming new substances.

• What some examples of physical changes?

Physical Change Examples

• Breaking or tearing


• Boiling or condensing


• Freezing or melting


• Sublimation


• Sublimation:

• “The change of state directly to a gas is known as sublimation.”

• “The reverse process is called deposition, the change of state from a gas directly to a solid.”

• From Modern Chemistry

Chemical Changes

• During chemical changes new substances are formed with different properties than the original substances.

• What is an example of a chemical change?

Chemical Change Example

• Heating baking soda, sodium hydrogen carbonate, forms sodium carbonate, carbon dioxide, and water. The formation of carbon dioxide is what causes cakes to rise.

Mixture or Pure Substance

• These bottles contain sodium chloride, sucrose, and a mixture of the two. Which is which and how can they be identified?

Physical and Chemical Properties

• What are some physical properties of this pen?

Physical Properties• Examples:

–Color–Hardness–Texture–Volume–Length–Mass

Physical Properties• More Examples:

–Density (mass/volume ratio)–Odor–Sound–Boiling point–Melting point–Magnetism

Physical Properties

• Melting Point and freezing point temperatures are the same.

Chemical Properties

• A chemical property is how something reacts.

• Does the pen float is physical.

• Does the pen dissolve is physical.

• Does the pen react with water is chemical.

Chemical Properties• Does the pen

burn is a chemical property.

• Whether and how something reacts is chemical.

Extensive vs Intensive

• Extensive Properties depend upon the amount of matter that is present.

• Intensive Properties do not depend on the amount of matter present. These properties are the same for a given substance regardless of how much of the substance is present.

• From Modern Chemistry

Extensive vs Intensive

• Which of the properties listed earlier are extensive and which are intensive?

• Comparisons of several properties are used together to identify an unknown.

Chemistry Vocabulary• A Symbol is a

representation of an element.

• One or two letters may be used.

• The first letter is upper case while the second is lower case.

H C O

Fe Cl Ag

Cu Ba Cf

Chemistry Vocabulary

• A formula is a representation of a molecule of an element or a molecule of a compound.

42

2

SOH

O


112212 OHC• The subscript

represents the number of atoms of a particular element in the molecule.

12 atoms of carbon

22 atoms of hydrogen

11 atoms of oxygen


42SOH• If no subscript

is shown. An understood one is indicated.2 atoms of hydrogen

1 atom of sulfur

4 atoms of oxygen

Chemistry Vocabulary• A coefficient is a

number in front of a formula and represents the number of molecules.

• If no coefficient is shown, one molecule is indicated.

112212 OH2C

2 molecules of sucrose

24 atoms of carbon

44 atoms of hydrogen

22 atoms of oxygen


wateroxygen Hydrogen

22 222

OHOH

• An equation is a sentence showing what is happening in a chemical

reaction.


O2H2 222 OH• The reactants are the substances

(elements or compounds) that will react. They are on the left or starting side.


OH 222 2O 2H

• The products on the right side of the equation are what are formed or are produced during the reaction.

Chemistry Vocabulary• An atom is the smallest unit of an

element that maintains the properties of that element. From Modern Chemistry– An atom is made up of electrons,

protons, and neutrons as well as other particles.• Protons and neutrons are made up of

quarks.

Chemistry Vocabulary• A atom is made up of a nucleus and

particles outside the nucleus called electrons.

• Electrons are negatively charged particles.

• The mass of an electron is about 1800 times smaller than that of the proton and neutron.

Chemistry Vocabulary• The nucleus is the tiny positive core

of the atom.

• Two of the particles in the nucleus are the proton and the neutron.

• The proton is a positively charged particle.

Chemistry Vocabulary• What is wrong with

this commonly used picture?

• The nucleus is 1/10000 times smaller than the atom.

• The atom is mostly empty space.

Chemistry Vocabulary• Proton:

– The charge on a proton is equal in magnitude but opposite in sign to the charge on an electron.

• A proton is made up of three quarks.– Two quarks have a +2/3 charge.– One quark has a -1/3 charge.

Chemistry Vocabulary• The mass of a proton is approximately

1800 times heavier than an electron.

• ***The number of protons present is what determines the type of atom.***– If the number of protons change, an

atom of a different element is formed.

Chemistry Vocabulary• The number of protons found in

the nucleus is known as the atomic number.–Hydrogen with an atomic number of

1 has only one proton. If it had 2, it would be helium.

–Uranium with an atomic number of 92 has 92 protons.


• A neutron is an uncharged particle found in the nucleus.

• The mass of a neutron is almost the same as the mass of a proton.

• A neutron is made of three quarks.– One quark has a +2/3 charge.

– Two quarks have a -1/3 charge.


• Two atoms of the same element can have differing numbers of neutrons. These are called isotopes.

• Hydrogen has three isotopes:– Hydrogen with 1 proton and 0 neutrons

– Deuterium with 1 proton and 1 neutron

– Tritium with 1 proton and 2 neutrons

Chemistry Vocabulary• The different masses of these

isotopes give them different properties such as melting and boiling points and reactivities and stabilities.

• Regular uranium is not radioactive enough for a nuclear fuel. Only certain isotopes of uranium will work.


• The mass number is the total number of protons and neutrons in the nucleus of the atom.

• The mass number is not found on the periodic table.

• The masses on the table are the weighted averages of the isotopes.

Chemistry VocabularyParticle Symbol Charge Mass

Number

Electron 1- 0

Proton 1+ 1

Neutron 0 1

p

-e

0n

Chemistry Vocabulary• Nuclear Symbol:• Mass Number

– Number of protons and neutrons

• Atomic number– Number of protons– Found on Periodic

Table

U23592

Chemistry Vocabulary• Number of protons =• 17• Number of neutrons =• 18• Number of electrons=• 17• The number of

protons = number of electrons

Cl3517


Mg2512

• Number of protons =• 12• Number of neutrons = • 13• Number of electrons=• 12


• In a neutral atom the number of protons is equal to the number of electrons.

• The number of protons can never vary in an atom.

• The electrons are the particles that can be gained or lost in a reaction.

Chemistry Vocabulary• The sum of the

positive protons and the negative electrons give the overall charge of the atom.

• The term charge was once called valence.

• The charge is shown as a superscript to the upper right.

2Mg

Chemistry Vocabulary• Number of protons =• 17• Number of neutrons =• 19• Number of electrons=• 18• (17+) + (?-) = 1-

– So ? = 18-

-3617 Cl

Chemistry Vocabulary• Number of protons =• 12• Number of neutrons =• 12• Number of electrons=• 10• (12+) + (?-) = 2+

– ?- = 10

22412 Mg

Chemistry Vocabulary• An ion is a charged atom or group of

atoms.

• A cation is a positively charged ion.

• An anion is a negatively charged ion. The prefix an- can mean not or negative.

Chemistry Vocabulary• Free state – The atom or molecule is

not combined with atoms of other elements.– Gold can be found in the free state.– Because of its reactivity, sodium cannot.

• Combined state – The atom is part of a compound.

Matter Unit• Now it is time to try “Chemistry Vocabulary

Worksheet: Application of Matter”.

• The exam will cover the material in this unit, the lab safety material, and the lab drawer equipment.

• Know the examples and how the ideas go together. Know all parts of the definitions.

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