CHAPTER 2 CHEMISTRY & LIFE

Organisms are composed of matter.Organisms are composed of matter. Matter takes up space and has mass. Matter takes up space and has mass. An element is a substance that cannot be broken down into other substances by chemical reactions.An element is a substance that cannot be broken down into other substances by chemical reactions. 92 naturally-occurring elements. 92 naturally-occurring elements. Each element has a unique symbol. Each element has a unique symbol. 1) Matter consists of chemicals in pure form (elements) and in combinations (compounds)

A compound is a substance consisting of two or more elements.A compound is a substance consisting of two or more elements. Table salt (sodium chloride or NaCl) is a compound. Table salt (sodium chloride or NaCl) is a compound. Pure sodium is a metal and chlorine is a gas, their combination forms an edible compound. Pure sodium is a metal and chlorine is a gas, their combination forms an edible compound.

Four elements - carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) - make up 96% of living matter (HONC!!!!) Four elements - carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) - make up 96% of living matter (HONC!!!!) Most remaining (4%) of an organism’s mass consists of phosphorus (P), sulfur (S), calcium (Ca), and potassium (K). Most remaining (4%) of an organism’s mass consists of phosphorus (P), sulfur (S), calcium (Ca), and potassium (K). Trace elements, e.g., iodine Trace elements, e.g., iodine 2) Life requires about 25 chemical elements

An atom is the smallest unit of matter.An atom is the smallest unit of matter. Atoms are small… teensy weensyAtoms are small… teensy weensy Atoms are composed of even smaller parts, called subatomic particles.Atoms are composed of even smaller parts, called subatomic particles. What are they?? 3) Atomic structure determines the behavior of an element

-Protons (+) -Electrons (-) Subatomic Particles of an Atom NeutronsNo charge1.009 Dalton* Protons (+) Dalton Electrons (-) 1/2000 Dalton Particle ChargeMass * Dalton: unit to express mass (1.66 x g) Helium ( 2 He)

Neon Atom ( Ne) 10 20

Atomic Number – Number of protons in an atom. This number is unique for each element. This number is unique for each element. The atomic number is written as a subscript before the symbol for the element (e.g. Helium = 2 He). The atomic number is written as a subscript before the symbol for the element (e.g. Helium = 2 He). In a neutral atom, In a neutral atom, the # of _________= the # of _________ the # of _________= the # of _________ Atomic number = number of protons = number of electrons Atomic number = number of protons = number of electrons Atoms and Molecules

Mass Number – # protons + # neutrons in an atom. The number of neutrons in an element can vary The number of neutrons in an element can vary (Isotopes). (Isotopes). The mass number is written as a superscript before the symbol for the element (e.g. Helium = He). The mass number is written as a superscript before the symbol for the element (e.g. Helium = 4 He). How does one calculate the number of Neutrons? How does one calculate the number of Neutrons? = the Mass Number - Atomic Number = the Mass Number - Atomic Number Atoms and Molecules

Examples:Examples:: The element sodium (Na) has a Mass Number of 23 ( 23 Na) and an Atomic Number of 11 ( 11 Na). How many Protons does Sodium have? How many Protons does Sodium have? How many Neutrons? How many Neutrons? How many Electrons? How many Electrons? Atoms and Molecules What about Carbon: C126 Or The Isotope of Carbon: C146

Atoms and Molecules - Elements occur as mixtures of isotopes. e.g., carbon -Different isotopes of the same element react in the same way. same way. -Some Isotopes are unstable and thus are radioactive.

Radioactive Isotopes - Elements occur as mixtures of isotopes. e.g., carbon 98.89% of carbon atoms have 6 neutrons ( 12 C). 1.11% of carbon atoms have 7 neutrons ( 13 C) % of carbon atoms have 8 neutrons ( 14 C). 12 C and 13 C are stable. 14 C is radioactive.

Electron Energy Levels: Electrons = Negatively (-) charged particles that orbit around the nucleus.Electrons = Negatively (-) charged particles that orbit around the nucleus. Electrons have orbitals.Electrons have orbitals. Each orbital is a certain distance from nucleus and can only contain 2 electronsEach orbital is a certain distance from nucleus and can only contain 2 electrons Orbitals the same distance from the nucleus are grouped into SHELLS (energy levels)Orbitals the same distance from the nucleus are grouped into SHELLS (energy levels)

Electron Orbitals and Electron-shell Configurations for Neon ( Ne) 10 20

The chemical behavior of an atom is determined by its electron configuration Elements in the periodic table are grouped together based on their valence shell electrons

Atoms with incomplete valence shells interact by either sharing or transferring valence electrons.Atoms with incomplete valence shells interact by either sharing or transferring valence electrons. These interactions hold atoms together by attractions called chemical bonds.These interactions hold atoms together by attractions called chemical bonds. A Molecule is two or more atoms held together by covalent bonds Atoms combine to form molecules

Chemical bond types:Chemical bond types: Covalent bonds = strong bond Covalent bonds = strong bond Ionic bonds = strong bond (but…) Ionic bonds = strong bond (but…) Weak bonds: Weak bonds: Hydrogen bonds Hydrogen bonds Van der Waal forces Van der Waal forces Atoms combine by chemical bonding to form molecules

A covalent bond is the sharing of pairs of electrons by two atoms.A covalent bond is the sharing of pairs of electrons by two atoms. If two atoms come close enough that their unshared orbitals overlap, each atom can count both electrons toward its goal of filling the valence shell. If two atoms come close enough that their unshared orbitals overlap, each atom can count both electrons toward its goal of filling the valence shell. Covalent Bonds Covalent Bonds

Every atom has a characteristic total number of covalent bonds that it can form - an atom’s valence. (HONC?)Every atom has a characteristic total number of covalent bonds that it can form - an atom’s valence. (HONC?) Hydrogen is 1. Hydrogen is 1. Oxygen is 2. Oxygen is 2. Nitrogen is 3. Nitrogen is 3. Carbon is 4. Carbon is 4.

- The attraction of an atom for the electrons of another atom is called its electronegativity. - Strongly electronegative atoms attempt to pull the shared electrons toward themselves. Electronegativity Scale (FYI): Electronegativity Scale (FYI): F = 4.0 F = 4.0 O = 3.5 O = 3.5 N = 3.0 N = 3.0 S and C = 2.5 S and C = 2.5 P and H = 2.1 P and H = 2.1 Li = 1.0 Li = 1.0 Covalent Bond Polarity

If electrons in a covalent bond are shared equally, it’s a nonpolar covalent bond.If electrons in a covalent bond are shared equally, it’s a nonpolar covalent bond. Covalent bond between two atoms of the same element is always nonpolar. Covalent bond between two atoms of the same element is always nonpolar. A covalent bond between atoms that have similar electronegativities is also nonpolar. A covalent bond between atoms that have similar electronegativities is also nonpolar. Because carbon and hydrogen do not differ greatly in electronegativities, the bonds of CH 4 are nonpolar. Because carbon and hydrogen do not differ greatly in electronegativities, the bonds of CH 4 are nonpolar. Nonpolar Covalent Bonds Electrons are shared EQUALLY.

If the electrons in a covalent bond are not shared equally by the two atoms, it’s a polar covalent bond.If the electrons in a covalent bond are not shared equally by the two atoms, it’s a polar covalent bond. O (3.5) is more electronegative than H (2.1) O (3.5) is more electronegative than H (2.1) Shared electrons spend more time around the more electronegative O atom. Shared electrons spend more time around the more electronegative O atom. Polar Covalent Bonds (-)(-) (-)(-) (+)(+)(+)(+)

Covalent bond summary: Atoms share electrons to fill valence shells Atoms share electrons to fill valence shells Nonpolar covalent bond Nonpolar covalent bond Atoms have same or similar electronegativity Atoms have same or similar electronegativity Polar covalent bond Polar covalent bond Atoms have dissimilar electronegativity Atoms have dissimilar electronegativity Gives molecule unique properties Gives molecule unique properties

If two atoms are VERY unequal in their electronegativity one atom strips an electron completely from the other.If two atoms are VERY unequal in their electronegativity one atom strips an electron completely from the other. E.g., sodium with one valence electron in its outer shell transfers this electron to chlorine with 7 valence electrons in its outer shell. E.g., sodium with one valence electron in its outer shell transfers this electron to chlorine with 7 valence electrons in its outer shell. Now, sodium has a full valence shell (the second) and chlorine has a full valence shell (the third). Now, sodium has a full valence shell (the second) and chlorine has a full valence shell (the third). Ionic Bonds Compounds formed by ionic bonds are called salts. Compounds formed by ionic bonds are called salts.

Examples: 1) Hydrogen 2) Ionic (weak in water) 3)Van der Waals Because these bonds are transient and easily broken, they can be used for: 1)Cell Signaling 2)Linking Molecules Together 3)3D shape Biologically Important Weak Bonds

Hydrogen Bonds H-bonds: formed by a charge attraction between a hydrogen atom that is covalently bonded to an electronegative atom and another electronegative atom. Weak Bond: only about 5% of the strength of a covalent bond -Allows water to remain as a liquid over a wide range of temperatures. - Causes surface tension

Van der Waal forces Van der Waals: attractions between small differences in polarity in a molecule. A very WEAK BOND and transient, highly affected by temp etc. A very WEAK BOND and transient, highly affected by temp etc.

The starting molecules are called reactants and the end molecules are called products.The starting molecules are called reactants and the end molecules are called products. In a chemical reaction, all of the atoms in the reactants must be accounted for in the products.In a chemical reaction, all of the atoms in the reactants must be accounted for in the products. Chemical Reactions Process of making and breaking chemical bonds The reactions The reactions must be must be “balanced.” “balanced.”