3minute Warm Up: A neutral Carbon Atom

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3-minute Warm Up A neutral Carbon Atom

• Draw a diagram of a neutral carbon atom. A
  neutral carbon atom has six protons in its
  nucleus. On your diagram, label the nucleus and
  electron cloud, and indicate the total positive
  or negative charge on each.

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Unit 2 Chemical InteractionsChapter 2 Chemical
Bonds and Compounds

• Section 1 Elements Combine to form Compounds

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Then and Now

• BEFORE, you learned
• Atoms make up everything on Earth
• Atoms react with different atoms to form
  compounds

• NOW, you will learn
• How compounds differ from the elements that make
  them
• How a chemical formula represents the ratio of
  atoms in a compound
• How the same atoms can form different compounds

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Set Learning Goals

• Students will
• Describe how compounds are made from combinations
  of atoms.
• Explain how chemical formulas represent
  compounds.
• Model a compound in an experiment.

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Section 2.1 Vocabulary

• Chemical formula
• Subscript

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EXPLORE Compounds (lab composition book

• How are compounds different from elements?
• MATERIALS
• carbon
• water
• sugar
• test tube
• test-tube holder
• candle
• PROCEDURE
• Examine the lump of carbon, the beaker of water,
  and the sugar. Record your
• observations of each.
• Carbon ________________________________________
• Water _________________________________________
• Sugar _________________________________________
• Pour some sugar into a test tube and heat it over
  a candle for several minutes. Record your
  observations.
• Observations ____________________________________
  __________________________________________________
  __________________________________________________
  __________________________________________________
  ______________________
• WHAT DO YOU THINK?
• The sugar is made up of atoms of the same
  elements that are in the carbon and water. How
  are sugar, carbon, and water different from one
  another?

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Compounds Properties are different than the
elements that make them

• Millions of compounds can be made from the 100
  elements in nature because of different ratios
  (like combining different letters of the alphabet
  to form words)
• Chemical bonds hold elements together
• The arrangement of elements will make different
  compounds

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Examples

• Carbon and hydrogen
• natural gas
• components of automobile gasoline
• the hard waxes in candles
• many plastics
• Each has a certain number of carbon and hydrogen
  atoms arranged in a specific way.

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More examples

• Hydrogen and oxygen
• Both are gases at room temp.
• Combined make water, a liquid
• Carbon, hydrogen, and oxygen
• Combined make sugar
• Calcium and chlorine
• Calcium soft metal
• Chlorine deadly gas
• Combined ice melter

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How do the properties of a compound compare with
theproperties of the elements that make it?

• They are often quite different.

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Atoms combine in predictable numbers

• A given compound always has a specific number of
  atoms
• Ammonia
• Always has 3 hydrogen atoms for each nitrogen
  atom a 31 ratio
• Hydrazoic acid also contains nitrogen and
  hydrogen, in a 13 ratio
• This means 1 hydrogen to every 3 nitrogen atoms

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Chemical Formulas

• Combination of chemical symbols in a given ratio
  to represent compounds
• Carbon dioxide has one carbon atom to two oxygen
  atoms
• Find the chemical symbols for each
• Oxygen O
• Carbon C
• Use subscripts (small numbers to the lower right)
  to show how many of each atom there are if
  there is no subscript, then there is one atom
• CO2
• One carbon, two oxygen

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How do we represent compounds?

• by a chemical formula

NaNO3 has how manyoxygen atoms?

• three

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• Which two atoms have the same elements?
• Methane and propane
• What makes them different compounds?
• Different ratios of atoms

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Why is the ratio of atoms in a chemical formula
so important?

• Different ratios of elements indicate different
  compounds.

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Same Elements, Different Compounds

• Different ratios make different compounds and
  they have different properties
• Nitrogen and Oxygen
• 11 NO
• 12 NO2
• 21 N2O
• Water and hydrogen peroxide
• Water H2O safe to drink and necessary for
  life
• Hydrogen peroxide H2O2 kills bacteria
• Test H2O2 on a potato will bubble, H2O will not

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Questions 2.2.1 (3rd section)

• KEY CONCEPTS
• 1. How do the properties of compounds often
  compare with the properties of the elements that
  make them?
• 2. How many atoms are in the compound represented
  by the formula C12H22O11?
• 3. How can millions of compounds be made from the
  atoms of about 100 elements?
• CRITICAL THINKING
• 4. Apply If a chemical formula has no
  subscripts, what can you conclude about the ratio
  of the atoms in it?
• 5. Infer How might you distinguish between
  hydrogen peroxide and water?