Elements, Compounds, and Molecules

Elements

All (living and nonliving) of the different kinds of matter in the universe is made from about 100 different substances, called elements.

Elements are called the building blocks of matter because all matter is composed of elements.

Each element is made up of the same type of atoms.

Compounds

A compound is a substance made of two or more different kinds of elements chemically combined in a specific ratio.

Each compound is represented by a formula that uses symbols to identify which elements are present.

A formula shows the ratio of elements in the compound.

H2O – ratio of Hydrogen is 2:1 Oxygen

The symbols make up the formula. A formula is just chemical shorthand for the compound.

The subscript lets us know how many atoms are present.

The coefficient lets us know how many molecules are present.

CompoundsCompounds

Molecules

A molecule is formed when two or more atoms join together chemically.

Diatomic molecules are made of two atoms of the same element.

Hydrogen – H2

Oxygen – O2

What is the difference between a compound and a molecule?

A molecule is formed when two or more atoms join together chemically.

A compound is a molecule that contains at least two different elements.

All compounds are molecules but not all molecules are compounds.

Molecular hydrogen (H2), molecular oxygen (O2) and molecular nitrogen (N2) are not compounds because each is composed of a single element.

Water (H2O), carbon dioxide (CO2) and methane (CH4) are compounds because each is made from more than one element.

Molecule

The smallest bit of each of these substances would be referred to as a molecule. For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen.

A single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

Molecule

When a compound is broken down into its’ smallest piece it is called a molecule. You should be able to write the formula for the following:

Water

Oxygen

Carbon Dioxide

Mixtures

Most matter in the universe is found in mixtures.

A mixture is made from two or more substances either elements, compounds or both - that are not chemically combined.

Mixtures and compounds differ

in two ways…

Substances in a mixture keep their individual properties.

Parts of a mixture are not necessarily present in specific

ratios.

Compound

A compound has properties different than the elements that make it up.

The parts of a compound are present in specific ratio’s.

Compounds and Mixtures

Most of the matter around you is in the form of compounds or mixtures.

Water, carbon dioxide, salt, vinegar, baking soda, lye, sugar, gasoline, and bleach are all chemical compounds.

Heterogeneous Mixture

A mixture in which different materials can be easily distinguished.

Pizza, dry soup, chex mix, trail mix are all examples.

Solutions

Homogeneous mixture: is a substance in which two or more substances are uniformly spread out. For example salt water.

Solution is another term for homogeneous mixture.

Solutions

Solute is the substance being dissolved.

Solvent is the substance that dissolves a solute.

Solubility is the amount of a substance (solute) that will dissolve in a solvent.

Example

Salt water:

The water is the solvent

NaCl is the solute

Colloids and Suspensions

A colloid is a heterogeneous mixture that like a solution never settles. Milk and smoke are examples.

One way to tell a colloid from a solution is because milk is appears white because its particles scatter light. Called the Tyndall Effect.

suspension

A suspension is a heterogeneous mixture containing a liquid in which visible particles settle.

River water

NaCl is the formula for salt

Water is H2O

An oxygen atom can bond with two hydrogen atoms to make a molecule we call water. Water is an example of a compound, because it contains more than one kind of atom. The formula for water is H2O, meaning there are two hydrogen atoms for each oxygen atom.

Carbon Dioxide CO2

Carbon dioxide molecules are made from one carbon and two oxygen atoms joined together by covalent bonds. The chemical symbol is CO2.

Glucose - C6H12O6

DNA

Is a large molecule made up of carbon, hydrogen, nitrogen, oxygen, and phosphorous.

Kinetic theory of matter

The idea that all matter is made up of constantly moving tiny particles.

Elements form compounds to try to fill their outer energy level with valence electrons.

This is called chemically stable. If the atom is not chemically stable it will lose, share, or gain electrons.

A chemical bond is the force that holds together the atoms in a substance.

Ion

An Ion is an atom or group of atoms that has become electrically charged.

A When an atom loses an electron it loses a negative charge and becomes a positive ion.

When an atom gains an electron, it gains a negative charge and becomes a negative ion.

Forming an Ionic Bond:

. Sodium has one valence electron and transfers that electron to chlorine

Na + Cl- the negative and positive electrical charges attract each other so the oppositely charged ions come together and form sodium chloride (salt).

An ionic bond is the attraction between two oppositely charged ions. This attraction is similar to the attraction between opposite poles of two magnets.

.

When two ions come together the opposite charges cancel out.

Compounds are electrically neutral. When the ions come together they do so in a way that balances out the charges on the ions

Molecules and Covalent Bonds

The attraction that forms between atoms when they share electrons is known as a covalent bond.