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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


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  • 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.


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  • 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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