The Chemistry of Life Chapter 2

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?

Answers

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

ProtonNeutronElectron Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons ____________________  Everything is made of _________________________  Matter is made of _________________________

The World of Elements C Different kinds of atoms = ______ _______ _______ _____ H ON PSNa K Mg Ca

Element A substance that cannot be broken down to other substances by ordinary _______ ______ _______ _______ means. Composed of only _______ kind of atom _______ naturally occurring

Atomic Number Number of protons (equals number of electrons) Examples: Carbon = _______ Calcium = _______

Mass Number Equal to the sum of its _____________________________ and _____________________________ 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 _____________________________ ; for example carbon-12 and carbon- __________________.

Life requires ~25 chemical elements About 25 elements are essential for life – Four elements make up 96% of living matter: _____________________________ _____________________________ – Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) sulfur (S) potassium (K)

Table 2.1 Naturally Occurring Elements in the Human Body

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

Figure 2.9 Energy levels of an atom’s electrons

Figure 2.10 Electron configurations of the first 18 elements

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

Figure 2.11 Electron orbitals

Bonding properties Effect of electrons – electrons determine chemical behavior of atom – depends on _____________________________ of _____________________________ in atom’s outermost shell _____________________________ shell How does this atom behave?

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?

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

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

Check Point 1.How many valence electrons are in Carbon? 2.How many valence electrons are in Phosphorus? 3.How many valence electrons are in Potassium? 4.How many shells are in Carbon? 5.How many shells are in Phosphorus? 6.How many shells are in Potassium?

Check Point Answers

– – – 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

– – H 2 (hydrogen gas) Covalent bond Bonds in Biology Weak bonds – _____________________________ bonds attraction between + and – – hydrophobic & hydrophilic interactions interaction with H 2 O – __________________________________________(ionic) Strong bonds – _____________________________ Hydrogen bond H2OH2O H2OH2O

Figure 2.14 Electron transfer and ionic bonding

Figure 2.15 A sodium chloride crystal

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

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

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

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

Figure 2.12 Covalent bonding in four molecules

Hydrogen bonding Polar water creates molecular attractions – attraction between _____________________________ H in one H 2 O molecule to _____________________________ O in another H 2 O – also can occur wherever an -OH exists in a larger molecule _____________________________ bond That’s Weak H O H

Figure 2.13 Polar covalent bonds in a water molecule

Figure 2.16 A hydrogen bond

Figure 2.17 Molecular shapes due to hybrid orbitals

Figure 2.19 A molecular mimic

Chemical reaction between hydrogen and oxygen

Figure 4.4 Variations in carbon skeletons

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?

Answers

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.

Post Assessment Answers