AP Biology The Chemistry of Life Chapter 2

AP Biology Pre Assessment 1. Name the 3 parts of an atom and their locations in an atom 2. What subatomic particle represents an atom’s atomic mass? 3. What units are used to measure the an atom’s mass? 4. What is the maximum number of electrons in an atom’s outer shell?

AP Biology Why are we studying chemistry? Chemistry is the foundation of Biology

AP Biology ProtonNeutronElectron Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons +0–  Everything is made of matter  Matter is made of atoms

AP Biology The World of Elements C Different kinds of atoms = elements H ON PSNa K Mg Ca

AP Biology Element  A substance that cannot be broken down to other substances by ordinary chemical means.  Composed of only one kind of atom  92 naturally occurring

AP Biology Atomic Number  Number of protons (equals number of electrons)  Examples: Carbon = 6 Calcium = 20

AP Biology Mass Number  Equal to the sum of its protons and neutrons  Example Sodium = atomic number 11 mass number 23 How many protons, neutrons and electrons?  Isotopes—atoms of the same element that differ in the number of neutrons; for example carbon-12 and carbon-14.

AP Biology Life requires ~25 chemical elements  About 25 elements are essential for life  Four elements make up 96% of living matter: carbon (C) hydrogen (H) oxygen (O) nitrogen (N)  Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) sulfur (S) potassium (K)

AP Biology Table 2.1 Naturally Occurring Elements in the Human Body

AP Biology Figure 2.5 Two simplified models of a helium (He) atom

AP Biology Figure 2.9 Energy levels of an atom’s electrons

AP Biology Figure 2.10 Electron configurations of the first 18 elements

AP Biology Check Point  What happens to energy as electrons move away from the nucleus?  What happens to energy as electrons move towards the nucleus?

AP Biology Figure 2.11 Electron orbitals

AP Biology Bonding properties  Effect of electrons  electrons determine chemical behavior of atom  depends on number of electrons in atom’s outermost shell  valence shell How does this atom behave?

AP Biology Bonding properties  Effect of electrons  chemical behavior of an atom depends on number of electrons in its valence shell What’s the magic number? How does this atom behave?

AP Biology Elements & their valence shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons)

AP Biology Elements & their valence shells Elements in the same column have the same valence & similar chemical properties Remember some food chains are built on reducing O to H 2 O & some on reducing S to H 2 S

AP Biology Check Point  How many valence electrons are in Carbon?  How many valence electrons are in Phosphorus?  How many valence electrons are in Potassium?  How many shells are in Carbon?  How many shells are in Phosphorus?  How many shells are in Potassium?

AP Biology Check Point  How many valence electrons are in Carbon? 4  How many valence electrons are in Phosporus? 5  How many valence electrons are in Potassium? 1  How many shells are in Carbon? 2  How many shells are in Phosporus? 3  How many shells are in Potassium? 4

AP Biology – – – Chemical reactivity Chem bond animation Chem bond animation  Atoms tend to  complete a partially filled valence shell or  empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds

AP Biology – – H 2 (hydrogen gas) Covalent bond Bonds in Biology  Weak bonds  hydrogen bonds  attraction between + and –  hydrophobic & hydrophilic interactions  interaction with H 2 O  van derWaals forces  (ionic)  Strong bonds  covalent bonds Hydrogen bond H2OH2O H2OH2O

AP Biology Figure 2.14 Electron transfer and ionic bonding

AP Biology Figure 2.15 A sodium chloride crystal

AP Biology Covalent bonds  Why are covalent bonds strong bonds?  two atoms share a pair of electrons  both atoms holding onto the electrons  very stable  Forms molecules – – H 2 (hydrogen gas) H — H H 2 O (water) H H Oxygen H H O

AP Biology Multiple covalent bonds  2 atoms can share >1 pair of electrons  double bonds  2 pairs of electrons  triple bonds  3 pairs of electrons  Very strong bonds H H–C–H H – – More is better!

AP Biology Nonpolar covalent bond  Pair of electrons shared equally by 2 atoms  example: hydrocarbons = C x H x  methane (CH 4 ) balanced, stable, good building block

AP Biology H H Oxygen Polar covalent bonds  Pair of electrons shared unequally by 2 atoms  example: water = H 2 O  oxygen has stronger “attraction” for the electrons than hydrogen  oxygen has higher electronegativity  water is a polar molecule  + vs – poles  leads to many interesting properties of water… + + – – – –

AP Biology Figure 2.12 Covalent bonding in four molecules

AP Biology Hydrogen bonding  Polar water creates molecular attractions  attraction between positive H in one H 2 O molecule to negative O in another H 2 O  also can occur wherever an -OH exists in a larger molecule  Weak bond  Bond animation Bond animation That’s Weak H O H

AP Biology Figure 2.13 Polar covalent bonds in a water molecule

AP Biology Figure 2.16 A hydrogen bond

AP Biology Figure 2.17 Molecular shapes due to hybrid orbitals

AP Biology Figure 2.19 A molecular mimic

AP Biology Chemical reaction between hydrogen and oxygen

AP Biology Figure 4.4 Variations in carbon skeletons

AP Biology Review 1. Which type of bond donates one electron from an atom to another? 2. When an atom loses an electron, what is it called? 3. When an atom gains an electron, what is it called?

AP Biology Review 1. Ionic bonds donate electrons~ opposite charges attract 2. Cation~ positively charged atom 3. Anion~ negatively charged atom

AP Biology Post Assessment 1. What is a trace element? 2. What is the maximum number of electrons in the 1s orbital? 3. What types of bonds form when 2 atoms are equally electronegative? 4. Provide an example of a compound.