What are elements?

1
What are elements?
On Earth, matter usually can be found as a
solid, liquid, or gas.
2
Elements and the Atomic Structure
3
Elements

• All matter is made elements.

• An element is a substance that cannot be broken
  down into simpler substances by physical or
  chemical means.

• Ninety-two elements occur naturally on Earth and
  in the stars.

4
Elements are Made of Atoms

• Each element has distinct characteristics.

• An atom is the smallest particle of an element
  that has all of the characteristics of that
  element.

5
Elements are Made of Atoms

• The nucleus, which is made up of protons and
  neutrons, forms the center of an atom.

• A proton (p) is a tiny particle that has mass
  and a positive electrical charge.

• A neutron (n0) is a particle with about the same
  mass as a proton, but it has no electrical charge.

• All atomic nuclei have a positive charge.

6
Elements are Made of Atoms

• The number of protons and neutrons in different
  atoms varies widely.

• The atomic number is the number of protons in an
  atoms nucleus.

• The mass number or atomic mass is the combined
  number of protons and neutrons.

7
Elements are Made of Atoms

• An electron (e) has little mass, but it has a
  negative electrical charge

• Surrounding the nucleus of an atom are smaller
  particles called electrons.

• An atom has an equal number of protons and
  electrons which produces an atom that has no
  overall charge.

8
Elements are Made of Atoms

• An energy level represents the area in an atom
  where an electron is most likely to be found.

9
Electrons in Energy Levels

• The number of electrons in the outermost energy
  level determines the chemical behavior of the
  different elements.

• Valence electrons are the outermost electrons in
  an atom.

• Elements with the same number of valence
  electrons have similar chemical properties.
• Group 1 has 1 valence electron. Group 2 has 2,
  etc

10
Isotopes

• The number of neutrons in the nuclei of an
  elements atoms can vary.

• Isotopes are atoms of the same element that have
  different mass numbers and the same chemical
  properties.

11
What Elements are Most Abundant?
12
Compounds

• A compound is a substance that is composed of
  atoms of two or more different elements that are
  chemically combined.

• Most compounds have totally different properties
  from the elements of which they are composed.
• Chemical bonds are the forces that hold the
  elements together in a compound creating a state
  of stability.

13
Compounds

• Covalent Bonds

• A covalent bond is the attraction of two atoms
  for a shared pair of electrons that holds the
  atoms together.

14
Compounds

• A molecule is composed of two or more atoms held
  together by covalent bonds.

• Covalent Bonds

15
Ions

• Ionic Bonds

• Positive and negative ions attract each other.
• An ionic bond is the attractive force between two
  ions of opposite charge.

16
Mixtures and Solutions

• A mixture is a combination of two or more
  components that retain their identities.

• When a mixtures components are easily
  recognizable, such as soil, it is called a
  heterogeneous mixture.
• homogeneous mixture such as chocolate milk, the
  component particles cannot be distinguished, even
  though they still retain their original
  properties.

17
Mixtures and Solutions

• A homogeneous mixture is also called a solution.

• A solution may be liquid, gaseous, or solid.

Examples of solutions -seawater -air