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Biology. Chapter 3 Section 1. Atoms. Smallest unit of matter that can not be broken down by chemical means. All matter is made up of atoms. Positively charges core surrounded by a negatively charged region. Atomic Structure. Atoms are made of three types of particles.

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biology

Biology

Chapter 3 Section 1

atoms
Atoms
  • Smallest unit of matter that can not be broken down by chemical means.
  • All matter is made up of atoms.
  • Positively charges core surrounded by a negatively charged region
atomic structure
Atomic Structure
  • Atoms are made of three types of particles.
  • Protons = positive charge
  • Electrons = negative charge
  • Neutrons = no charge
slide4

Atoms have no overall charge because each has the same # electrons and protons.

  • (-) = (+) in a neutral atom
  • Protons and neutrons are in the nucleus
  • Electrons are around the nucleus in a region called the electron cloud
element
Element
  • A substance made up of atoms that have the same number of protons.

example: Each atom of the element carbon has 6 protons.

Atoms of an element can have different number of neutrons. These atoms are isotopes.

chemical bonds
Chemical Bonds
  • Electrons are arranged in levels around the nucleus.
  • The levels farthest from the nucleus can usually hold 8 electrons.
  • The electrons in the outermost level are valance electrons.
slide7

Atoms tend to combine with each other so that eight electrons will be in the valance shell.

  • Chemical bonds form between groups of atoms because most atoms become stable when they have eight electrons in the valence shell.
covalent bonding
Covalent Bonding
  • Atoms bond by SHARING electrons.
  • A group of atoms held together by covalent bond is a molecule.
  • Example: Water
ionic bonding
Ionic Bonding
  • Atoms losing or gaining electrons
  • Losing electrons cause a positive charge
  • Gaining electrons cause a negative charge
  • Ion- an atom or group of atoms that has an electric charge
  • Ionic bond- the attractive force between oppositely charged ions
  • Example: Salt (NaCl)
polarity
Polarity
  • In some covalent bonds, the shared electrons are attracted more strongly to one atom than to another.
  • This results in one end having a partial negative charge and the opposite having a partial positive charge.
  • Molecules with partial charges on opposite ends are said to be polar.
solubility
Solubility
  • Nonpolar dissolves in nonpolar
  • Polar dissolves in polar
  • “Like dissolves like”
  • Example: sugar or salt in water
  • Example: oil in water
hydrogen bonds
Hydrogen Bonds
  • Are stronger than attractions between other molecules, but not as strong as a covalent bond.
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