UNIT: Matter

Objectives: Lesson 3 of 4• You will understand the difference between an element and a

compound• You will learn how bonds form between atoms• You will learn the difference between a molecule and a compound• You will understand the difference between heterogeneous and

homogeneous mixtures

TOPIC: Elements, Compounds & Mixtures

QuickwriteIn 1-2 sentences answer one of the questions below:• What do you think the difference is between an

element and a compound?• When you drink water, do you think it mostly made up

of one type of element or a combination of elements?• If you drink a sports drink such as Gatorade, do you

think it mostly made up of one type of molecule or mixture of molecules?

Elements• All elements can be found on

the periodic table• Elements are substances

made of only one type of atom

• They are the simplest forms of matter

• Elements cannot be broken down into simpler substances

• Elements cannot be physically separated

• For example, pure Gold contains only Gold atoms

• Pure Carbon (graphite) contains only Carbon atoms

Elements

= He

• Have you ever inhaled helium to alter voice?

• If so, you inhaled a pure substances made of only one type of atom

• In other words, you inhaled Helium as a pure element

What is an Element?

• Substances made of only one type of atom• They are the simplest forms of matter and cannot be broken

down into simpler substances• Example: Gold (Au), Carbon (C)

+-+ -

Bonds Between Atoms• A chemical bond is when two atoms share or transfer electrons• Consider the two hydrogen atoms below• When two hydrogen atoms get close enough, a bond may form• The result is a molecule of hydrogen gas or H2

Bond

Bonds Between Atoms

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Fluorine Atom Sodium Atom

Bond

Some bonds form when

electrons are actually

Transferred from one atom

to the other

For example when Sodium bonds with Fluorine to make

Sodium Fluoride (NaF), the electron is completely removed from the sodium atom

What is a Chemical Bond?• A chemical bond is when two atoms share or transfer electrons• Example: molecule of H2 or NaF

+-+ -

Bond

Compounds• A Compound is a pure

substance made up of two or more elements that are bonded together

• For example, consider common table salt, sodium chloride

• Sodium (Na) Chloride (Cl) forms when the element sodium bonds with the element Chlorine; forming a new chemical compound

• Or, consider water• Water forms when Hydrogen

(H) bonds with Oxygen (O)

2

Molecules vs. Compounds• A molecule is two or more atoms

bonded together• A compound is substance made

up of two or more kinds of different elements that are bonded together

• So what is the difference between a molecule and compound?

• For example, Air is made up of oxygen O2 and nitrogen N2 molecules

• Because they are made up of only one kind element, they can only be molecules and NOT compounds

= O2

= N2

Water

= Water (H2O)

• A molecule is two or more atoms bonded together

• A compound is a substance made up of two or more kinds of different elements that are bonded together

• For example water (H2O) is a compound because it contains two elements: hydrogen and oxygen bonded together

• Water (H2O) is also a molecule because it is made of two or more atoms bonded together

• Because it meets both definitions, water (H2O) is both a molecule and a compound

• Therefore, all compounds are molecules, but not all molecules can be compounds

Molecules vs. Compounds

What is the difference between a molecules and a compound?

• A molecule is two or more atoms bonded together, Example: O2 , O3 and N2

• A compound is substance made up of two or more kinds of different elements that are bonded together Example: H2O

Chemical Formulas• A chemical formula is used to represent a compound• A chemical formula is a group of symbols that shows

the number and kinds of atoms in a compound• For example, in sodium chloride, or salt the chemical

formula is NaCl• By writing NaCl, this tells us the compound contains

one sodium atom and is chemically bonded to one chlorine atom

• Let’s take a look at the chemical formula for water: H2O

• The chemical formula for water tells us that the compound contains two hydrogen atoms bonded to one oxygen atom

2

What is a chemical formula?• Used to represent a compound, it is a group of symbols that

shows the number and kinds of atoms in a molecule or compound

• Example: NaCl & H2O

Determine how many atoms of each element are in each compound below:

• CaCl2

• Answer: The above compound CaCl2 contains one calcium atom and two chlorine atoms

• O3

• Answer: The above compound O3 contains three oxygen atoms• (NH4)2S• Answer: The above compound (NH4)2S contains two nitrogen

atoms atoms 2 x (1N) = 2N, 8 hydrogen atoms 2 x (4H) = 8H, and one sulfur atom 1 x (1S) = 1 S

Practice:

Mixtures• Most matter you see is a mixture• A mixture is two or more

substances mixed together• Take salt and water for example• If you were to mix these two

compounds, Salt (NaCl) + Water (H2O) you would create a mixture

• The air you breathe is actually a mixture of mostly Oxygen gas (O2) + Nitrogen gas (N2) + and Argon

Salt

Water

= O2

= N2

= Ar

What is a Mixture?• One or more substances that are mixed together not

bonded to one another• Most types of matter are mixtures• Ex: Salt + water (NaCl + H2O)

• In a homogeneous mixture, the substances are evenly mixed

• Once again, consider the air we breathe

• Recall that Air is a mixture of mixture of mostly Oxygen gas (O2) + Nitrogen gas (N2) + and Argon

• These molecules/atoms are evenly mixed, every breathe you take is the same as the one before it

• The molecules and atoms are also far too small to be seen and therefore CANNOT be individually selected and “picked” out with your hand

= O2

= N2

= Ar

Homogeneous vs. Heterogeneous Mixture

Salt Water

Mixture

• Consider another homogeneous mixture of salt and water

• Notice, the salt and water molecules throughout the mixture are evenly mixed

• If you were to drink the homogeneous mixture of salt water, every sip would most likely taste the same as the previous sip before it

• Just like in the last mixture, the atoms/molecules are far too small to be seen and therefore CANNOT be “picked” out

• In other words, you can’t individually pick out the salt atoms/molecules with your hand

= Water (H2O) = Sodium (Na) = Chlorine (Cl)

Homogeneous vs. Heterogeneous Mixture

• A heterogeneous mixture is when one or more of the substances are NOT mixed evenly

• Often times, in a heterogeneous mixture, the objects are large enough to be seen and therefore CAN be picked out

• Consider a heterogeneous mixture of sand and water

• Notice, the molecules throughout the mixture are NOT evenly mixed

• The sand particles in the mixture are large enough to be seen and CAN be individually selected and “picked” out by hand

= Sand (SiO2)= Water (H2O)

Water &Sand

Mixture

Homogeneous vs. Heterogeneous Mixture

• Consider another heterogeneous mixture of Oil and Water (H2O)

• Notice, the molecules throughout the mixture are NOT evenly mixed

• That is, the oil molecules are not mixing with the water molecules

• If you were to drink this mixture, each sip would most likely taste different than the previous sip before it

= Oil Molecule= Water (H2O)

Oil &Water

Mixture

Homogeneous vs. Heterogeneous Mixture

What is the difference between a Homogeneous vs. Heterogeneous Mixture?Homogeneous mixture Heterogeneous mixture

Mixed evenly Mixed unevenlySubstances cannot be seen or “picked out”

Substances can sometimes be seen and “picked out”

Ex: Salt + water Ex: Water + Sand

Summarize:(you can always write you own)

• Compare and contrast the following types of matter: element, compound and mixture

• Describe the components of an atom

• How many atoms are in the compound Al2O3

• Draw the flow chart seen to the right: