Atoms by dfhdhdhdhjr



• Atoms – The basic unit of matter.
 Atoms are very small, made up of
 subatomic particles that are even
 smaller than the atom. Atoms are
 neutral they have no charge.

• Protons-
 Have about the same mass as a neutron.
 Have a positive charge
 Contained in nucleus in the center of the atom
• Atoms have the same number of protons as electrons
• Neutrons
 Have about the same mass as a proton.
 Have no charge, are neutral
• Contained in nucleus in the center of the
• Electrons
 Negatively charged particle
 Electrons are in constant motion
 They move around the out side of the nucleus
 Atoms have the same number of protons as
 Electrons are in orbits around the nucleus
 The first orbit can hold 2 electrons
• The second orbit can hold up to eight electrons
• Element-
 is a substance composed of only one
  type of atom
 more than 100 elements
 Elements are represented by one or two
  letter symbol
• Sum of protons and neutrons in nucleus is
  called atomic mass
  Periodic Table

• Atomic Number - Simply refers to the
  number of protons present in the atom.
• Element Symbol - This is the symbol that
  chemical formulas or equations use to
  indicate that certain element.
• Atomic Mass - The average mass of one
  atom of that element in amu's (Atomic Mass
• Isotopes-
 Have different
•          number of neutrons
 They have the same
•           number of electrons & protons
• All chemical properties such as bonding
  remain the same

Chemical compounds
 Substance formed by two or more elements
 Formed in definite proportions
 Properties of compound is different that the
 elements its formed by
 Hydrogen and oxygen are gases at room
 temperature, when combined they from water a
 liquid at room temperature.
Chemical Bonds-
 Atoms in a compound are held together
  by chemical bonds
 Bonds are formed by the electrons in
  the area around the nucleus
• The electrons that are available to from
  bonds are called valence electrons

Covalent bonds
 Strongest bonds
 Shared electrons
    Single covalent Bond

•Two electrons are shared
   Double covalent bond

•Four electrons are shared

• Ions
 Ions are formed by giving up or
  receiving an electron
 Ions can have a positive charge or
  negative charge
 If atom gives an electron it has a
  positive charge called a Cation
• If atom gains an electron it has an negative
  charge called an Anion
Ionic Bonds
Formed when one or more electrons
are transferred from one atom to the
Van der Waals Forces

• Van der Waals Forces
 Not all electrons are shared equally
  when bonds are formed
 When sharing is unequal then the
  molecule may be slightly positive or
 A slight attraction between molecules
  can develop because of oppositely charged

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