Atoms, Elements,

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Atoms, Elements, Compounds

• Biology II
• D. Mitchell

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Atom

• smallest unit of matter that cannot be broken
  down.

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Atomic Structure

• Atoms consist of 3 kinds of subatomic particles
• electrons- negatively charged subatomic particles
  that occupy the outer electron shells
• protons- positively charged subatomic particles
  that occupy the nucleus of an atom.
• neutrons- subatomic particles that have no charge
  (neutral) and occupy the nucleus of an atom.

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Bohrs Atomic Model
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Parts of an atom
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• ATOMS have a neutral charge because of its equal
  number of positively charged protons and
  negatively charged electrons.

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• Different energy levels (electron cloud) can hold
  a certain numbers of electrons. Atoms are most
  stable when the outermost energy level is full!

Electron level of electrons
1 2
2 8
3 18
4 32
5 50
6 72
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(2)Element

• a substance made of one kind of atom
• can not be broken down to other substances by
  chemical means.

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• 91 elements naturally occur on Earth.
• Life requires about 25 chemical elements.
• Oxygen, Carbon, Hydrogen, and Nitrogen make up
  96 of the human bodys mass.

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• Elements in the Human Body
• Element Symbol Element Symbol
• 1 Oxygen O 6 Phosphorus P
• 2 Carbon C 7 Potassium K
• 3 Hydrogen H 8 Sulfur S
• 4 Nitrogen N 9 Sodium Na
• 5 Calcium Ca
• Most abundant to least abundant

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Periodic Table of Elements

• Lists the following information
• Name of element
• Symbol
• Atomic number the number of protons. (The
  number of protons the number of electrons.)
• Atomic mass (Mass Number) the number of protons
  plus the number of neutrons in the nucleus.

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(3) Compound

• substance made of two or more elements bonded
  together in a fixed ratio.
• represented by a chemical formula that identifies
  the elements in the compound and their
  proportions.
• properties are different from the properties of
  the elements that make up the compound

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Examples

• (1) NaCl -Sodium Chloride
• composed of the elements Sodium(Na) and
  Chlorine (Cl)
• (2) H2O Water
• composed of the elements Hydrogen(H) and Oxygen
  (O)
• (3) C3H6O3 Glucose
• composed of the elements Carbon (C), Hydrogen
  (H), and Oxygen (O)

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Chemical Bonds
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• Atoms are the basic building blocks of matter.
• Atoms join with other atoms to form stable
  substances.
• The attraction between atoms is a result of their
  positive or negative charges.
• Atoms join to form compounds and molecules.

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• Electrons determine whether an atom will bond.
• The number of electrons in the outermost electron
  shell(valence electrons) determine how many bonds
  can be formed.

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Oxidation numbers

• indicates the number of electrons lost, gained,
  or shared as a result of chemical bonding

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What is a chemical bond?

• A chemical bond is formed when electrons from two
  atoms interact and join.

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• When atoms with incomplete outer shells interact,
  they share, receive (gain), or donate (lose)
  electrons.

• Types of Chemical Bonds
• Ionic Bond
• Covalent Bond
• Hydrogen Bond

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Ionic Bonds

• Occur when one atom gains or loses a valence
  electron.
• Atoms that lose electrons are positively charged.
• Atoms that gain electrons are negatively charged.
• The oppositely charged ions are attracted to each
  other.

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• Characteristics
• Form between metals and nonmetals
• Ionic compounds tend to form salts.
• Ionic compounds dissolve easily in water .
• Ionic compounds easily conduct electricity.

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Covalent Bonds

• A COVALENT BOND results when two atoms "share"
  valence electrons between them.
• This most commonly occurs when two nonmetals bond
  together.
• Covalent bonds form molecules (O2 , H2) and
  compounds (CO2)

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Hydrogen Bonds

• A hydrogen bond is a bond formed due to a weak
  attraction between polar molecules of opposite
  charge
• As the name "hydrogen bond" implies, one part of
  the bond always involves a hydrogen atom.
• Hydrogen bonds hold the two strands of the DNA
  together.

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Why are chemical bonds important?

• The type of chemical bond that occurs in a
  molecule or substance in part defines its
  structure, appearance, and properties.
• Example
• NaCl and HCl
• Both contain Cl
• Table salt and hydrogen chloride