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Biology

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

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  1. Biology Chapter 3 Section 1

  2. 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

  3. Atomic Structure • Atoms are made of three types of particles. • Protons = positive charge • Electrons = negative charge • Neutrons = no charge

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Covalent Bonding • Atoms bond by SHARING electrons. • A group of atoms held together by covalent bond is a molecule. • Example: Water

  9. 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)

  10. 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.

  11. Solubility • Nonpolar dissolves in nonpolar • Polar dissolves in polar • “Like dissolves like” • Example: sugar or salt in water • Example: oil in water

  12. Hydrogen Bonds • Are stronger than attractions between other molecules, but not as strong as a covalent bond.

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