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CHAPTER 2 CHEMISTRY & LIFE

CHAPTER 2 CHEMISTRY & LIFE. Organisms are composed of matter. Matter takes up space and has mass. An element is a substance that cannot be broken down into other substances by chemical reactions. 92 naturally-occurring elements. Each element has a unique symbol.

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CHAPTER 2 CHEMISTRY & LIFE

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  1. CHAPTER 2 CHEMISTRY & LIFE

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

  3. A compound is a substance consisting of two or more elements. 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.

  4. 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). Trace elements, e.g., iodine 2) Life requires about 25 chemical elements

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

  6. Subatomic Particles of an Atom Particle Charge Mass -Protons (+) -Electrons (-) * Dalton: unit to express mass (1.66 x 10-24g) Helium (2He)

  7. Neon Atom ( Ne) 20 10

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

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

  10. Atoms and Molecules Examples:: The element sodium (Na) has aMass Numberof23 (23Na) and anAtomic Numberof11 (11Na) . How many Protons does Sodium have? How many Neutrons? How many Electrons? 12 C What about Carbon: 6 14 C OrThe Isotope ofCarbon: 6

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

  12. Radioactive Isotopes -Elements occur as mixtures of isotopes. e.g., carbon 98.89% of carbon atoms have 6 neutrons (12C). 1.11% of carbon atoms have 7 neutrons (13C). 0.0000000001% of carbon atoms have 8 neutrons (14C). 12C and 13C are stable. 14C is radioactive.

  13. Electron Energy Levels: Electrons = Negatively (-) charged particles that orbit around the nucleus. Electrons have orbitals. Each 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)

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

  15. 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

  16. Atoms with incomplete valence shells interact by either sharing or transferring valence electrons. These interactions hold atoms together by attractions called chemicalbonds. A Molecule is two or more atoms held together by covalent bonds Atomscombine to formmolecules

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

  18. 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. Covalent Bonds

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

  20. - 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): F = 4.0 O = 3.5 N = 3.0 S and C = 2.5 P and H = 2.1 Li = 1.0 Covalent Bond Polarity

  21. Nonpolar Covalent Bonds • 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. • 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 CH4 are nonpolar. Electrons are shared EQUALLY.

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

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

  24. 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. 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.

  25. 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: Cell Signaling Linking Molecules Together 3D shape Biologically Important Weak Bonds

  26. 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

  27. 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.

  28. 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. Chemical Reactions Process of making and breaking chemical bonds • The reactions must be “balanced.”

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