Of Atoms and Molecules: Chemistry Basics

1. Of Atoms and Molecules: Chemistry Basics Chapter 2

2. MATTER – The basis for everything All organisms consist of matter and energy. LIFE- based on chemical principles.

3. A. Matter Material that takes up space. Matter broken down to pure substances- Elements 1. Elements Pure chemical substances composed of atoms. • Examples? • Oxygen, sodium, copper, potassium • How many elements exist? (92)

4. How many of these elements are essential to life? (25) • The essential elements are divided into: • Bulk elements: needed in relatively large amounts • Examples: C, O, H, N • Trace elements: needed in relatively small amounts • Examples: Fe, K, Na, Zn, Ca

5. Periodic Table of Elements

7. 2. Atom The smallest “piece” of an element that retains the characteristics of that element. Composed of 3 subatomic particles: • Protons • Neutrons • Electrons

8. Atoms of each element – characteristic number of protons # of protons – determines size and character of each atom. Charge- attraction between opposite types of particles. Atom – electrically neutral Electron – small compared to proton and neutron Orbital- location for an electron relative to its nucleus.

9. Element – has a symbol. He- Helium Na- Sodium Atomic number- shows the # protons in the atom- identity of the atom. Elements are arranged sequentially in the periodic table by atomic number.

10. Characteristics of Subatomic Particles

11. Atomic number • # protons in nucleus of an atom (establishes identity of the atom) • Since most atoms are electrically neutral, atomic number indicates # of electrons as well. Atomic mass • # protons plus # neutrons in nucleus of an atom

12. Periodic table information on carbon: Atomic mass given in table is average mass of all the element’s isotopes.

13. How can we determine the number of neutrons in an atom? • # neutrons = atomic mass - atomic # • Determine # neutrons in a carbon atom (atomic mass = 12; atomic # = 6). • # neutrons = 12 - 6 = 6 Do all carbon atoms have the same number of protons? Do all carbon atoms have the same number of neutrons?

14. Isotopes • Atoms having the same number of protons, but differing numbers of neutrons. • Same charge & characteristics but different masses. • Often one isotope is very abundant and others are rare. • If an isotope is unstable, it is termed radioactive Ex. Carbon isotopes • carbon 12 (12C) 6 neutrons • carbon 13 (13C) 7 neutrons • carbon 14 (14C) 8 neutrons

15. Atoms bound together – molecules 3. Compound A pure substance formed when atoms of different elements bond. The number of atoms of each element is written as a subscript. Examples: • CO2 carbon dioxide • H2O water • CH4 methane • C6H12O6 glucose

16. 4. Molecule Smallest piece of a compound that retains characteristics of that compound. The number of molecules is written as a coefficient. Examples: • 4CO24 molecules of carbon dioxide • 2C6H12O62 molecules of glucose • 6O26 molecules of oxygen

17. Chemical Reactions • The reactants of a reaction are written to the left of the arrow. • The products of a reaction are written to the right of the arrow. Example: 6O2 + C6H12O6 6H2O + 6CO2 + energy

18. 5. Chemical Bonds • Type of bond formed is determined by the number of valence electrons in the interacting atoms [octet rule]. • The goal of chemical bonding is for all atoms involved to complete or eliminate their outer electron shells.

20. a) Covalent bonds- form when atoms share electron pairs. • strongest type of bond • tend to form when atoms have 3, 4 or 5 valence electrons • the number of electron pairs shared determines whether the covalent bond is single, double or triple • can be nonpolar or polar

22. Nonpolar covalent bonds - electrons are shared equally between atoms. Ex. methane

23. Types of diagrams to represent molecules

24. Polar covalent bonds - electrons are not shared equally. They are drawn more strongly to 1 atom’s nucleus than the other. Form when less electronegative atoms bond with more highly electronegative atoms. Ex. water

25. b) Ionic bonds- form when oppositely charged ions are attracted to each other. • weaker than covalent bonds • atoms with 1, 2 or 3 valence electrons give up electrons to atoms with 7, 6 or 5 valence electrons which forms ions • form salts which break apart in water Ex. NaCl

26. c)Hydrogen bonds- form when opposite charges on two molecules are attracted to each other. • weakest type of bond* Ex. DNA H2O

27. 6. Attractive forces • van der Waals attraction • Attraction between molecules or within molecules that occur when oppositely charged regions approach each other • Often used to shape molecules

28. Interactions with water hydrophobic:parts of a molecule that do not have charges cannot interact with water hydrophilic:parts of a molecule that have charges can interact with water

29. B. The Importance of Water 1. Properties • Cohesion- the attraction of water molecules for each other. • Adhesion- the attraction of water molecules for other compounds. • Imbibition– the tendency to absorb water and swell

30. High heat capacity – takes a great deal of heat to raise the temperature of water. • High heat of vaporization - a lot of heat is required to evaporate water. • Exists as solid, liquid or gas - solid (ice) is less dense than liquid.

31. 2. Solutions A solution is a mixture of one or more solutes dissolved in a solvent. If solvent is water, then it is an aqueous solution. Water is a strong solvent because it separates charged atoms or molecules.

32. 3. Acids & Bases • Acids - substances that add H+ to a solution. • Bases - substances that remove H+ from solution. • Buffer systems: help stabilize pH pH scale is measure of acidity/alkalinity based on H+ concentration.