Combinations of Atoms • There are 92 naturally- occurring elements in the universe. • Like letters of the alphabet, different atoms of different elements combine, or bond, to form different types of matter. • Compounds are made up of two or more different elements bonded together.
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Combinations of Atoms There are 92 naturally-occurring elements in the universe. Like letters of the alphabet, different atoms of different elements combine,
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Combinations of Atoms• There are 92 naturally-occurring
elements in the universe.• Like letters of the alphabet, different
atoms of different elements combine, or bond, to form different types of matter.
• Compounds are made up of two or more different elements bonded together.
• Compounds are different than the atoms they are made of.
Chemical Properties• Depending on the elements in a
compound, a compound may react with other compounds.
• Iron will rust when exposed to oxygen and water, but it won’t if it is melted and mixed with chromium and nickel metals to make stainless steel.
Bonds
Chemical Bonds
• Chemical bonds are forces that hold the atoms together in compounds.
• Bonds typically form when atoms share or transfer electrons.
Electron Energy Levelsa) Atomic number = number of protons in the
nucleus. Since protons are positive in charge, the nucleus attracts an equal number of negative electrons.
b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels.
c) Electron energy levels determine how an atom behaves when it encounters other atoms.
Electrons are placed in energy levels according to rules:
1) The 1st energy level can hold up to two electrons.
2) The second energy level can hold up to eight.
3) After that some more complicated rules apply. You will learn these rules later.
4) The outermost energy level always attempts to stabilize with eight electrons. It does this by sharing or transferring electrons.
5) The electrons in the outermost energy level are called “valence electrons.”
Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons in the last level.• C would like to
• N would like to• O would like to
gain 4 electronsgain 3 electronsgain 2 electrons
Why are electrons important?• Elements have different electron
configurations.– A configuration is just an
arrangement.– Different electron configurations
mean different levels of bonding.– A carbon atom looks like this: