Science 8 4TH QTR Exam Notes

Ionic & Metallic Bond

• Understanding Ions

  • Nonmetals share valence electrons to form compounds.
  • Metals transfer valence electrons to nonmetals during bonding.
  • Electron transfer leads to noble gas electron configurations.
  • Ions are atoms that gain or lose valence electrons.
  • Ions are no longer electrically neutral.
  • Losing electrons results in a positive charge.
  • Gaining electrons results in a negative charge.

• Losing Valence Electrons

  • Metals become stable by losing valence electrons when bonding with nonmetals.

• Gaining Valence Electrons

  • Nonmetals gain valence electrons from metals or share with other nonmetals.
  • This helps them achieve a noble gas electron arrangement.

• Determining an Ion’s Charge

  • Atoms are neutral with an equal number of protons and electrons.
  • Ions gain or lose electrons, resulting in a charge.
  • Charge is determined by subtracting the number of electrons from the number of protons.
  • Example: Nitrogen ion: 7 protons – 10 electrons = -3 charge, written as $N^{3-}$.

Ionic Bonds – Electron Transferring

• Nonmetal atoms GAIN electrons LOST by metal atoms when forming a chemical bond.
• The attraction between positively and negatively charged ions forms a stable ionic compound.
• An ionic bond is the attraction between oppositely charged ions.

Ionic Compounds

• Usually solid and brittle at room temperature.
• Have relatively high melting and boiling points.
• Many dissolve in water.
• Aqueous solutions conduct electricity due to ion mobility.
• Covalent compounds, like water, are made of molecules. Ionic compounds have a large collection of oppositely charged ions, not molecules.

Comparing Ionic and Covalent Compounds

• Covalent compounds are made up of molecules.
• Ionic compounds consist of a large collection of oppositely charged ions held together by ionic bonds.

Metallic Bonds – Electron Pooling

• Metal atoms combine valence electrons.
• A metallic bond is formed when metal atoms share pooled valence electrons.
• Valence electrons are not bonded to one atom but move freely among ions.

Properties of Metallic Compounds

• Metals are good conductors of thermal energy and electricity.
• Valence electrons can move freely to conduct electric charge.
• Metals are malleable and ductile because ions can slide past each other in the electron sea.
• Metals are shiny due to the interaction of valence electrons with light.

Elemental Carbon and Simple Organic Compounds

• Living things contain carbon, hydrogen, oxygen, nitrogen, phosphorus (CHONPS), and other elements.
• Carbon compounds comprise about 18% of living organisms.
• Most compounds in or on your body contain carbon (excluding water and salts).

Organic Compounds

• Originally thought to come from living organisms.
• Now defined as chemical compounds containing carbon atoms bonded to at least one hydrogen atom.
• May also contain oxygen, phosphorus, or sulfur.
• Carbon dioxide ($CO_2$) and carbon monoxide ($CO$) are not organic due to the absence of a carbon-hydrogen bond.

Understanding Carbon

• Carbon uniquely combines with other atoms to form millions of compounds.
• Atomic number is 6 (6 protons and 6 electrons).
• Has 4 valence electrons.
• Achieves chemical stability through covalent bonding.

*RECALL: Covalent Bond – a chemical bond formed by sharing one or more pairs of electrons between atoms.

What makes Carbon unique? (Not in book)

1. Having 4 valence electrons (tetravalency)
   • allowing multiple bonding opportunities
2. Catenation – ability to form long chains/rings
   • offering infinite variety of structures
3. Formation of functional groups
   • offering a chance to form chemicals of varied reactivity and functionality
4. Hybridization and Molecular Geometry
   • providing opportunity to form varied molecular geometry contributing to structural complexity

The Carbon Group

• Silicon and germanium also have four valence electrons and form four covalent bonds.
• Requires more energy for them to bond compared to carbon, so less likely to occur.

The Forms of Pure Carbon

1. Graphite

   • Hexagonal rings of carbon atoms in sheets held by weak forces.
   • Atoms form thin sheets that slide or bend easily.
   • Used as a lubricant and in golf clubs, tennis rackets, and pencil lead.

2. Diamond

   • Each carbon atom bonds tightly to four others.
   • Rigid, orderly structure makes diamonds extremely strong.
   • Used in jewelry, drill bits, and saw blades.

3. Fullerene

   • Carbon atoms form cage-like structures.
   • One form is a ball-like structure of 60 carbons.
   • Also forms tubelike structures called carbon nanotubes.
   • Discovered late in the twentieth century, uses are still being explored.
   • Future uses may include faster, smaller electronic components.

4. Amorphous Carbon

   • Atoms lack a distinct structure.
   • Found in soot, coal, and charcoal.

   *WORD ORIGIN: amorphous from a- and Greek morphe, means “without form”

Hydrocarbons

• A compound containing only carbon and hydrogen atoms.
• Methane ($CH_4$) is the simplest hydrocarbon.

Hydrocarbon Chains

• Carbon atoms link in straight chains, branched chains, or rings.
• Isomers have the same molecular formula but different structural arrangements.
• Each isomer is a unique molecule with its own name and properties.

Carbon-to-Carbon Bonding

• Single bond: two carbon atoms share two electrons. A hydrocarbon with only single bonds is an alkane.
• Double bond: two carbon atoms share four electrons. A hydrocarbon with at least one double bond is an alkene.
• Triple bond: two carbon atoms share six electrons. A hydrocarbon with at least one triple bond is an alkyne.

Saturated Hydrocarbons

• Contain only single bonds.
• No more hydrogen atoms can be added.

Unsaturated Hydrocarbons

• Contain one or more double or triple bonds.
• Additional hydrogen atoms can bond if double and triple bonds break.

Naming Hydrocarbons

• Names indicate the number of carbon atoms in each molecule.

*CARBON CHAINS

• 1ST STEP: Find the longest carbon chain and count the number of carbon atoms.
• 2nd STEP: Choose the root word for the hydrocarbon according to how many carbon atoms it has.
• 3rd STEP: Choose the suffix according to the largest number of bonds in the molecule.
• All single bonds  -ane
• At least one double bond  -ene
• At least one triple bond  -yne

Determine the Prefix

• Hydrocarbons sometimes have a prefix, and sometimes they do not.
• If a hydrocarbon contains a ring structure, the prefix -cyclo is added before the root name.

*CARBON ATOMS: | NAME: 1 meth- 2 eth- 3 prop- 4 but- 5 pent-

*CARBON ATOMS: | NAME: 6 hex- 7 hept- 8 oct- 9 non- 10 dec-

• Note that hydrocarbons sometimes have other prefixes and numbers added before their name, however, this naming system is in more advanced chemistry courses.

Summary on Naming Hydrocarbons:

1. Examine the Compound
2. Count the number of carbon atoms in the longest continuous chain.
3. Determine the root name of the hydrocarbon using the list of Root Words.
4. Determine the type of bonds in the hydrocarbon, then use the list of Bond Type and Hydrocarbon Suffix to find the suffix.
5. Put the root and the suffix together to name the hydrocarbon.
6. If the hydrocarbon is a ring, add -cyclo to the beginning of the name.

Other Organic Compounds

• Substituted Hydrocarbons
• Other atoms can be substituted for a hydrogen atom in a hydrocarbon.
• A substituted hydrocarbon is an organic compound in which a carbon atom is bonded to an atom, or group of atoms, other than hydrogen.
• Organic compounds function differently when hydrogen atoms are substituted with other atoms.

Functional Groups

• The substitution of a hydrogen atom in organic compounds with other atoms causes the substituted hydrocarbon to have new properties.
• A functional group is an atom or group of atoms that determine the function and properties of the compound.
• The substituted hydrocarbon is renamed to indicate which functional group has been substituted.

Hydroxyl Group

• Rubbing alcohol is the common name for the compound 2-propanol.
• 2 Propanol is a substituted hydrocarbon of propane and contains the hydroxyl functional group.
• Its formula is -OH.
• Organic compounds that contain the hydroxyl group are called alcohols.
• Alcohols are polar compounds and can dissolve in water.
• Alcohols have high melting and boiling points and are commonly used as disinfectants, fuels, and solvents.
• Larger alcohols form when the hydroxyl group is substituted in larger hydrocarbons.
• Substituting a Hydrogen (H) atom for a functional group in a hydrocarbon changes its properties.

Halide Group

• The halide group contains group 17 halogens – fluorine, chlorine, bromine, and iodine.
• An example of this is bromomethane, in which a bromine atom replaces one of the hydrogen atoms in methane.
• Its formula is R-X.
• Notice the prefix -bromo is before the hydrocarbon name to form the name bromomethane.
• Bromomethane, sometimes called methyl bromide is a pesticide and can be used to kill pests in the soil before strawberries are planted. Its use is strictly regulated because of its environmental hazards.

*WORD ORIGIN – halide from Greek hals; means “salt”

Carboxyl Group

• A carboxyl group consists of a carbon atom with a single bond to a hydroxyl group and a double bond to an oxygen atom.

• Its formula is -COOH.

• When a carboxyl group replaces a hydrogen atom in a hydrocarbon, the result is a carboxylic acid.

• Citric acid in citrus fruits, such as oranges, lemons, and limes, is a carboxylic acid.

• Dairy products such as buttermilk and yogurt also contain a carboxylic acid called lactic acid.

• Two simple carboxylic acids are methanoic acid and ethanoic acid.

• Methanoic acid (HCOOH)

  • Methanoic acid is in the toxin of stinging ants. Methanoic acid is also known as formic acid.

• Ethanoic acid ($CH_3$

• Ethanoic acid is in vinegar, which is used in many food items including salad dressings and pickles. Ethanoic acid is also known as acetic acid.

Amino Group

• The amino group consists of a nitrogen atom covalently bonded to two hydrogen atoms and its formula is -$NH_2$
• The suffix -amine is added to the end of each root name to indicate that the amino group is in the compound.
• The amine, methylamine, forms when an amino group is substituted for a hydrogen in methane.
• Notice that -yl follows the root name meth.
• If a hydrocarbon, such as methane, loses a hydrogen atom, its name changes to methyl. If ethane loses a hydrogen atom, its name becomes ethyl.

Shapes of Molecules

• Molecules come in different shapes and sizes.
• Knowing a molecule’s shape helps scientists understand how it interacts with other molecules, how strong the bonds are between atoms, and what type of bonds are in the molecule.
• Molecules are not flat. They are three-dimensional.
• Molecular Shapes:
  1. Tetrahedral – Methane is an example of a tetrahedral molecule. The atoms in a tetrahedral molecule form a pyramid.
  2. Planar – Ethene is an example of a planar molecule. The atoms in a planar molecule are all on the same plane.
  3. Linear – Ethyne is an example of a linear molecule. The atoms in a linear molecule form a straight line.

Polymers

• The word plastic is a common term that refers to a type of substance called a polymer.
• A polymer is a molecule made up of many of the same small organic molecules covalently bonded together, forming a long chain.
• A monomer is one of the small organic molecules that make up the long chain of a polymer.
• Some polymers occur naturally, but many are made in laboratories.
• Polymers occurring in nature are called natural polymers.
• Polymers made in laboratories are called synthetic polymers.
• Many synthetic polymers are made from simple hydrocarbons by a process called polymerization.
• Polymerization is the chemical process in which small organic molecules, or monomers, bond together to form a chain.
• Polyethylene is a polymer used to make shampoo bottles, grocery bags, and toys.
• It is made by the polymerization of ethene – also known as ethylene.

Formation of a Polymer

• The double bonds are broken in the ethylene molecules
• After the bonds break, the electrons in each molecule are free to form new bonds.
• Long chains of ethylene molecules form, creating the polyethylene polymer.

Synthetic Polymers

• Polyethylene and many other synthetic polymers are made from petroleum.
• Petroleum is a thick, oily, flammable mixture of solid, liquid, and gaseous hydrocarbons. It is an example of a fossil fuel, and occurs naturally beneath Earth’s surface.
• It formed from the remains of ancient, microscopic marine organisms.
• Many common objects are made of synthetic polymers.