ATOMS

What is an atom?• Atoms are the fundamental

building blocks of all things• Atoms are the most basic unit

of matter

Atoms are made up of protons, neutrons, and electrons

- Protons: particles with a positive charge; can be found in the nucleus

- Neutrons: particles with no charge (a neutral charge); can be found in the nucleus

- Electrons: particles with a negative charge that can be found orbiting the nucleus in the electron cloud

• The atomic number equals the number of protons.

• The electrons in a neutral atom equal the number of protons.

• The mass number equals the sum of the protons and neutrons.

Where are electrons found?Electrons exist in orbitals or energy levels 2 electrons fit in the first energy level8 electrons fit in each subsequent energy level

2 neutrons2 protons2 electrons

6 neutrons6 protons6 electrons 2 in first level, 4 in second

Helium (He) Carbon (C)

• The charge indicates the number of electrons that have been lost or gained.

• A positive charge indicates the number of electrons (which are negatively charged) that have been lost.

• A negative charge indicates the number of electrons that have been gained.

• This structure can be written as part of a chemical symbol.

Check for Understanding

•With your partner, answer the following question:–If an element has a NEGATIVE

charge, has it lost or gained electrons?–Time: 30 seconds

A chemical element is a pure substance that consists entirely of one type of atom. Elements are mapped on the periodic table.

Do all atoms of the same element always have the same number of neutrons?

Answer: NO

Atoms of the same element with differing numbers of neutrons are called isotopes

• The combinations of two or more elements in definite proportions form a chemical compound.

• Naming compounds (molecular formulae):H20 = 2 parts hydrogen to 1 part oxygen

Compounds and their properties

• The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed.

• Example:– Sodium is a silverish metal– Chlorine is a greenish gas– Sodium Chloride (NaCl) is table salt

Impress Ms. Moloney• Can you and your partner come up with one

other compound whose properties are very different from the properties of the individual elements that make up the compound??

How atoms in compounds are brought together

• Ionic bonds are formed when one or more electrons are transferred from one atom to another

• Example: Sodium Chloride (NaCl)

How atoms in compounds are brought together

• Covalent bonds are formed when electrons are shared between atoms

• A molecule is the structure that results when atoms join together by covalent bonding

• Example:• H2O (Water)• HCl (Hydrogen Chloride)• CO2 (Carbon Dioxide)

Van der Waals Forces

• When molecules are close together, the oppositely charged regions are attracted to each other.

• Van der Waals Forces are the slight forces of attraction

• These forces explain why a gecko can climb up vertical surfaces (suction cup like forces)