+ SBI4U BIOCHEMISTRY Ms. Manning Atoms, Bonding & Molecular Polarity

+ “... Everything that living things can do can be understood in terms of the jigglings and wigglings of atoms.” Richard P. Feynman, 1963 Sperm approaching an egg

Atoms, Bonding, and Molecular Polarity

6 types of atoms make up 99% of all living organisms ElementSymbolAtomic # % of human body weight OxygenO865.0 CarbonC618.5 HydrogenH19.5 NitrogenN73.3 CalciumCa201.5 PhosphorusP151.0 PotassiumK190.4 SulfurS160.3 SodiumNa110.2 ChlorineCl170.2 MagnesiumMg120.1 Naturally Occurring Elements in the Human Body

+ MATTER All MATTER is made up of tiny little particles called ATOMS. Just like cells are the basic unit of life… Atoms are the basic unit of matter.

+ MATTER Atoms are the basic unit of matter An atom is made up of a central nucleus which contains protons and neutrons. The nucleus is surrounded by a cloud of electrons, which are orbiting around the nucleus.

+ 6 C Carbon Mass Number = protons + neutrons The element carbon - 6 th element in the periodic table Symbol Atomic Number = # of protons = # electrons

Bohr model of a hydrogen and oxygen atom Shells Nucleus Protons Neutrons Subatomic Particles

Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 8 neutrons 6 electrons 6 protons 7 neutrons Isotopes are atoms of the same element that vary in the number of neutrons. Because they have the same number of electrons, all isotopes of an element have the same chemical properties.

Why are electrons so important? The chemical behavior of an atom is determined by its electron configuration – that is, the distribution of electrons in the atom’s electron shells. The chemical behaviour of an atom depends mostly on the number of electrons in its outermost shell. (= valence electron/shell) All atoms with incomplete valence shells are chemically reactive.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to H would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons Gain 1 electron

Atoms bond to form compounds Compounds are made up of at least 2 different kinds of atoms (e.g., H 2 O) Bonds are formed by the sharing or transfer of electrons 2 Types of Chemical Bonds Ionic Bonds Covalent bonds

Ionic Bonds – occur when one atom donates or gives up one or more electrons Ionic Compound ( Na + Cl - ) Salt crystals Opposite charges attract to form ionic bonds

Reaction between Na and Cl to form ionic sodium chloride (salt)

Covalent Bonds – involve a sharing of a pair of valence electrons between atoms. Figure. 1.5, p.10

Single covalent bond Double covalent bond Four single covalent bonds Two single covalent bonds

Covalent bond between H 2 and O to form one molecule of water (H 2 O)

2 Types of Covalent Bonds Polar CovalentNon-polar covalent Equal sharing of electrons Unequal sharing of electrons All bonding types are determined by the atoms ELECTRONEGATIVITY E.g., H 2 O 2 E.g., H 2 O

Electronegativity the measure of the relative abilities of bonding atoms to attract electrons (Pauling Scale) Electronegativity = Stronger pull of shared electrons The periodic table has electronegativity values. We can determine the nature of a bond based on Δ EN (electronegativity difference).

Electronegativity In a non-polar covalent bond, there is relatively no electronegative difference. Electrons are shared equally. E.g., O 2 oxygen atoms have the same elecronegativity In a polar covalent bond, there is an electronegative difference. Electrons are shared unequally. E.g., H 2 O oxygen atom is more electronegative than the hydrogen atoms

Calculating the Electronegative Difference Δ EN = higher EN – lower EN NBr3: Δ EN = 3.0 –2.8 = 0.2 (for all 3 bonds). Basically: a Δ EN…  below 0.5 = covalent (equal é sharing)  = polar covalent (unequal é sharing)  above 1.7 = ionic (loss/gain of é)

Calculate electronegativity( Δ EN): Determine the Δ EN and bond type for: HCl Br 2 CrO CH 4 H 2 O KCl

The boy is not equally sharing with anyone else but rather taking all the food for himself. Polar Covalent Bond Analogy

Non-Polar Covalent Bond Analogy The children are equally sharing the drink between themselves.

Ionic Bond Analogy Parents giving up their money to keep stable when their children beg to gain cash

Water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen. Shared electrons spend more time near the the oxygen nucleus As a result, the oxygen atom gains a slightly negative charge and the hydrogen atoms become slightly positive

Polar Molecules (like water) have an unequal distribution of charge. Since water is polar, it can attract other water molecules. The attraction between water molecules are called hydrogen bonds. Hydrogen bonds are weak forces between molecules

Electronegativity and Physical Properties Electronegativity can help to explain properties of compounds like those in the lab. Lets look at HCl: partial charges keep molecules together.

The situation is similar in NaCl, but the attraction is even greater ( Δ EN = 2.1 vs. 0.9 for HCl. Which would have a higher melting/boiling point? Electronegativity and Physical Properties

Solubility of Substances in Water Cl - Water Cl - Na + Water Na + Due to water’s polarity, it is a great solvent. A solvent is a substance in which a solute dissolves. A solute is what is being dissolved. What is happening in the example below? Water is great at dissolving both ionic (+,-) compounds and polar (partial positively, partial negatively charged molecules) molecules.

Solubility of Substances in Water Hydrophilic (means water-loving) compounds interact with water by dissolving in it. E.g., Anions (chloride ions) in salt attracted to + poles of water (causes sodium cation to dissociate) Hydrophobic (means water-hating) compounds do not interact with water because they cannot form hydrogen bonds E.g., Non-polar compounds are insoluble in water Oil – non-polar compound of carbon and hydrogen

Choice Board Task: Atoms, Bonding and Molecular Polarity Task: Demonstrate your understanding of the relationship between electronegativity, bonding, and the polarity of molecules.

Success Criteria: Incorporate, at least, the following terms in your product: Include examples and/or diagrams where appropriate. Ensure that your product is self-explanatory (provide explanations for visual elements where appropriate) Prepare to present to a group of your peers References (APA) Electron(s)Atom(s)ProtonsNeutrons Molecules Valence shell or valence electron Covalent bondIonic bond CationAnionElectronegativity Non-polar covalent bond Polar covalent bond Hydrogen bond Electronegative difference Reactivity or reactive HydrophilicHydrophobic Soluble/Solubilit y Insoluble IsotopeCompound Intra- and inter- molecular forces Polar molecule

Choice Board LOGICAL- MATHEMATICAL Create a flow chart or matrix Be sure to study the criteria carefully before you select and as you proceed. BODILY-KINESTHETIC Construct a model, or representation (include a written explanation) VISUAL SPATIAL Design a graphic organizer (e.g., concept map with connecting phrases between words ) WILD CARD INTERPERSONAL Write a short story that incorporates characters and a plot. MUSICAL-RHYTHMIC Create a rap, jingle or song INTERPERSONAL Develop a role play, an oral presentation, or a YouTube video VERBAL LINGUISTIC Create a poem, poster or print advertisement Choose a mode to express your understanding :

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