Atoms and Molecules

The stuff life is made of.

Atoms

Crucial points:

An atom is the smallest unit of an element.

Atoms are made up of electrons, protons, and neutrons.

Electrons orbit in energy shells (also called valence shells). The electrons in the outer shell are most important to forming bonds between atoms.

An atom is the smallest unit of an element.

Each element has distinct properties (color, melting point, reactivity, etc.)

Properties arise from the basic atomic structure of each element.

Atoms are made up of sub-atomic particles.

Electrons Protons

Neutrons

Electrons orbit in energy (valence) shells

Bonding: Ionic

Ionic bonds involve the transfer of electrons from one atom to another.

Ionic bonds are strong bonds.

Ionically-bonded atoms tend to form crystaline structures rather than individual molecules.

Ionically-bonded substances tend to be soluble in water.

Bonding: Ionic

Bonding: Ionic

Why are these called ionic bonds?

When an atom has the same number of electrons as protons, it is electrically neutral but…

When an atom has one more electron than protons, it has a negative charge. If it has one less electron than protons, it has a positive charge. Atoms with an electrical charge are called ions.

Isotopes

Isotopes are also different forms of the same atom.

Different isotopes have the same number of protons and electrons, but different numbers of neutrons.

Bonding: Covalent

Covalent bonds involve sharing of electrons between atoms.

Covalent bonds result in individual molecules.

Covalent bonds may be:Neutral

Polar

Bonds: Covalent

Two hydrogen atoms share electrons, forming a covalent bond

Bonds: Covalent

In a water molecule, the oxygen atom tends to keep the shared electrons longer than the hydrogen atoms,

creating a polar covalent bond.

+ +

- -

Bonds: Hydrogen

Hydrogen bonds are weak bonds that form and break easily.

Hydrogen bonds link molecules together.

Hydrogen bonds are electrical attractions between polar molecules.

Bonding: Hydrogen

Here, water molecules form hydrogen bonds with oneanother. The positive end of one molecule is attracted to the

negative end of the next.

Bonding: Hydrogen

Here, sugar molecules (polar) are in a solution with water (also polar). Where would hydrogen bonds form?

Recap

Atoms are the basic units of an element.

Atoms bond together to form molecules.

Ionic bonds are electrical attractions between ions.

Covalent bonds involve sharing of electrons between atoms.

Covalent bonds form discreet molecules.

Hydrogen bonds link molecules together.