Chapter 2 The Nature of Molecules

What’s The Matter? Anything that has mass and occupies space is matter Matter is composed of atoms

Bohr Model- Very Simple and Unrealistic

Atomic Mass vs Atomic Number Atomic Number= Number of Protons Atomic Mass = Number of Protons + Number of Neutrons Measured in Daltons – Measured in Daltons and also equal to 1 gram

Are All Atoms Created Equal? NOPE- Most atoms have no net charge because the number of protons and electrons are equal. Ions- are charged due to a surplus of either electrons or protons –More electrons is a negatively charged ANION –More protons is a positives charged CATION

What is an Isotope?

Radioactive Isotopes- when nuclei are unstable and break up into smaller elements. –Half-Life- the amount of time it takes for ½ of an element to decay. **If you have a 14 gram sample of Carbon and the Half-Life of Carbon is 5,600 years How many grams of Carbon would you have in 22,200 years?** Answer= grams

Do We Know Exactly Where Electrons Are? Nope, but we can make a good guess. Orbital- the area around the nucleus where an electron can LIKELY be found

Atoms Always Want to Move From Higher Energy to Lower Energy Lowest energy closest to the nucleus Highest energy farthest from the nucleus. Lowest to highest Energy- s, p, d, f –S can hold 2 electrons –P can hold 6 –D can hold 10 –F can hold 14

Practice Problems Find the electron configurations for Nitrogen, Selenium, and Krypton

Oxidation vs Reduction Oxidation= Loss of an electron Reduction = Gain of an electron

Mendeleev Mendeleev created the periodic table and organized it according to how the outer electrons of elements interacted. Atoms tend to completely fill their outer electron level with 8 electrons.

Ionic Vs Covalent Bonds Ionic- form when atoms with opposite electrical charges attract –Form salts and crystals Covalent- shares electrons, has no net charge, no free electrons, and the octet rule is satisfied. –Can have single, double, or triple covalent bonds

Chemical Reactions Things that affect the rate of chemical reactions Temperature= increase temperature increase rate Concentration of Reactants and Products- proceed to equilibrium Catalysts- Lower activation energy to speed reactions.

Water Water Everywhere PropertyExplanationBenefit to Life CohesionHydrogen bonds hold water molecules together Leaves pull water upward from the roots High Specific heatH+ bonds absorb heat when they break and release heat when they form Water stabilizes the temp or organisms and the environment. High Heat of Vaporization Many H+ bonds must be broken for water to evaporate Evaporation cools body surfaces Lower Density of IceLakes do not freeze solid SolubilityPolar water molecules are attracted to ions and polar compounds, making them soluble Many kinds of molecules can move freely in cells, permitting a diverse array of chemical reactions

pH Acids- has more H+ pH of 0-6 Bases- has more OH- pH of 8-14 Neutral= pH of 7 Buffer- acts as a reservoir for hydrogen ions donating them to a solution when their concentration falls taking them from the solution when their concentration rises