Chemistry Review: Atoms

Transcription

1 Chemistry Review: Atoms Atoms are made up : nucleus containing protons and neutrons orbitals containing electrons (2, 8, 8,...). Valence electrons outermost electrons

2 Chemistry Review: Atoms All atoms of a particular element have the same number of protons (Atomic Number) Mass number: number of P +N.

3 Isotopes Isotopes are atoms that have the same number of protons (therefore the same element), but have a different mass number due to a different number of neutrons in the nucleus.

4 Radioisotopes Radioisotopes are isotopes that can sometimes be unstable and reactive and can spontaneously break apart or decay. Carbon has three isotopes, the most common carbon-12, carbon-13 and the most reactive carbon-14 (used in carbon dating of fossils). Hydrogen has hydrogen-1, hydrogen-2 and the most reactive hydrogen-3.

5 Ions Ion: Atom which gains or loses an electron and becomes charged Metals lose electrons to form cations (+) Nonmetals gain electrons to form anions (-)

6 Intramolecular Forces bonds between atoms within a molecule (within molecules) Intermolecular Forces bonds between atoms of different molecules (between molecules)

7 Intramolecular Bonds Ionic Bonds: A force of attraction between a cation and an anion (aka a transfer of electrons). Ex. NaCl

8 Intramolecular Bonds Covalent Bonds: neither atom is willing to give up electrons so the electron pairs are shared (i.e. two non-metals). ex. H 2 (g), CH 4 (g)

9 Intramolecular Bonds Double and triple bonds can result if 2 or 3 pairs are shared. l ex. O 2, N 2, CH 2 CH 2

10 Non metals always make a certain number of covalent bonds (based on their need for valence electrons). Number of bonds

11 Electronegativity Elements have varying electronegativity (EN) or the affinity (want for) electrons. Non-polar covalent bond: the atoms involved have similar electronegativities, so the electrons are shared equally. (ex. C-H).

12 Electronegativity Polar covalent bonds: the atoms involved have different electronegativities so there is uneven sharing of electrons. This results in a separation of charge. (ex. O-H)

13 Electronegativity the more electronegative atom (often O, N, S) will pull the electron pair towards it more often and gain a partial negative charge. The electrons spend more time away from the more electropositive atom (often H), so it has a partial positive charge.

14 Polar Covalent Molecules If the molecule is asymmetrical and has a polar covalent bond, the molecule will also be polar. ex. H 2 O, CH 3 OH

15 Non-polar Covalent Molecules Non polar molecules occur when a molecule has non polar covalent bonds OR because of the symmetrical arrangement of polar covalent bonds.

16 Intermolecular Bonds The partial charges on polar covalent molecules result in attraction between molecules. Ex. Hydrogen bonds: a force between an atom with a partial negative charge and and a hydrogen atom with a partial positive charge

17 Hydrogen Bonds in Water

18 Water Water is polar (versatile solvent) Like dissolves like Polar molecules- dissolve in water Hydrophilic (water loving) Non-polar molecules- do not dissolve in water- Hydrophobic (water fearing) clump together instead- hydrophobic effect

19 Questions 1. Explain how a polar covalent bond is different from an ionic bond. 2. Use a water molecule to describe the relationships among all of the following: polar and non-polar molecules, intramolecular and intermolecular forces, hydrophilic and hydrophobic interactions.

20 Organic Compounds Organic compounds: chemicals of life, contain a lot of Carbon ex. C 6 H 12 O 6 (usually also hydrogen, but not always) Hydrocarbons: only contain C and H, ex. CH 4 Inorganic compounds do not contain Carbon ex. HCl

21 Water Water is inorganic (no Carbon) but it is an important chemical to life!

22 Functional Groups Other elements attach to the carbon backbone of organic compounds. These groups are more reactive and give certain chemical properties to the molecule.

23 Functional Groups

24

25 Practice Questions Identify the circled functional groups

26 n Identify as many functional groups as you can:

27 Organic Compounds Carbon atoms attach to each other to form chain and ring structures that are the backbones of the major biological molecules (carbohydrates, lipids, proteins, and nucleic acids). flashanimat/carbohydrates/glucose.swf

28 Functional Groups ex. -OH, -COH, -CO and -COOH are polar because of the highly electronegative oxygen atom, making compounds that contain them (alcohols and sugars) highly soluble in water.