Elements & Atoms Element: a substance that can neither be broken down nor converted to another substance by chemical reactions. Pure substance that contains only one type of atom
Figure 2.1a Atomic number (number of protons) Mass number (number of protons plus neutrons) Element symbol 12 6 C He Ne SeBr Cl F Ar Kr Xe O N C B S P Si Al I Ge AsGa TeSbSnIn Mn Cr Po At RnPbBiTI Co FeV Cu Ni Zn TmYb Lu Ho ErDy Be Li Mg Na K ScCaTi MoNbRuTcPdRh Ag Y Sr RbZr H Cd LaBa TaHfOs Re IrW AuPt HgCs Bh Sg Mt Hs Rg Ds Cn Fr Ac Ra Rf Db MdNo Lr Es FmCfAm Cm Bk NpPuU EuGd Tb Pm Sm Nd Pa Pr Th Ce
Figure 2.1b Thermometers, dental fillings and batteries Mercury in the air settles into water. It can pass through the food chain and build up in fish, shellfish and animals that eat fish. Exposure to high levels can damage the brain and kidneys. Can damage the kidneys and the nervous system, and interfere with development of the brain in the very young children Mercury
Figure 2.1c Deficiencies of copper can cause premature hair graying, sterility and premature wrinkling of the skin.
Figure 2.1d Affects nearly all system: Hearing loss, kidney problems, lower IQ, children are more vulnerable because they tend to place things in their mouths. Houses built before ‘78, present toys, pipes, faucets Lead
Trace elements are common additives to food and water –Without iron, your body cannot transport oxygen –An iodine deficiency prevents production of thyroid hormones, resulting in goiter -Deficiencies of copper can cause premature hair graying, sterility and premature wrinkling of the skin.
Electron cloud Protons 2e – Nucleus Electrons Mass number = 4 Neutrons Atoms consist of protons, neutrons, and electrons Electrons are kept in orbit by the attraction between the negatively charged electrons and positively charged protons Atomic number: 2 (number of protons) Mass number: 4 (sum of the number of protons and neutrons in its nucleus
Atomic Number C 12 Mass number (atomic weight) ( # Protons + # Neutrons) 6 Atomic Number (# of Protons in an atom) Atomic Symbol (Carbon) The atomic number determines which element it is. # protons = atomic number # electrons = atomic number (in an uncharged atom) # neutrons = mass number – atomic number
Atomic Weight (Mass Number) May Vary Isotope: a variant form of an atom with same number of protons but different numbers of neutrons Naturally occurring carbon 99%~1%Minute quantities Stable isotopes Radioactive: the nucleus decays
Radioisotopes in Medicine & Research when radioactive compounds are used in metabolic processes, they act as radioactive tracers An imaging instrument that uses positron- emission tomography (PET) detects the location of injected radioactive materials Normal Alzheimer’s
C isotope studies can be used to identify areas with histories of vegetation change How the Maya were able to sustain such large populations is still a question today. Use of Carbon Isotopes in Determining Ancient Maya Land Use Jungle: C 3 Plants Discriminate more against CO 2 containing 13 C isotope Maize: C 4 Plants
Why is the energy emitted in radioactive decay hazardous?.
Radioactive Isotopes Can Harm Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA. The 1986 Chernobyl nuclear accident released large amounts of radioactive isotopes. Naturally occurring radon gas may cause lung cancer.
Electron arrangement determines the chemical properties of an atom Only electrons are involved in chemical activity Electrons occur in energy levels called electron shells The number of electrons in the outermost shell determines the chemical properties of an atom
The number of electrons in the valence shell (outermost shell) determines the chemical properties of the atom Elements whose outer shells contain unfilled orbitals are chemically reactive When all the orbitals are filled, the element is inactive (inert)
An uncharged atom of gold has an atomic number of 79 and a mass number of 197. This atom has _________ protons, _______ neutrons, and __________ electrons. a. 79 …118 …79 b. 118 …79 …118 c. 276 …118 …79 d. 79 …276 …79
The most abundant element found in the human body by weight is _________. a. oxygen b. carbon c. fluorine d. hydrogen
Isotopes of atoms differ in their number of __________. a. neutrons b. electrons c. protons d. atomic nuclei
Na Sodium atom Transfer of electron Cl Chlorine atom Ionic bonds are attractions between ions of opposite charge The octet rule: atoms are most stable when their outer most energy shells are either full or empty Ions: atoms electrically charged as a result of gaining or losing electrons Complete transfer of electrons. Attraction between ions of opposite charge
Na Sodium atom Transfer of electron Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) + – Na + Cl –
Covalent bonds join atoms into molecules through electron sharing A covalent bond results when atoms share outer-shell electrons –A molecule is formed when atoms are held together by covalent bonds
Covalent Bonds The number of covalent bonds an atom can form is equal to the number of additional electrons it needs to fill its valence shell –A single bond forms when two electrons are shared between two atoms –A double bond forms when four electrons are shared between two atoms –A triple bond forms when ______ electrons are shared between two atoms
Electrons are Unequally Shared in Polar Covalent Bonds Fig 2.8 Oxygen draws shared electrons towards itself Oxygen becomes “a little” negative Hydrogens become “a little” positive Results in Hydrogen Bonds between neighboring molecules Water molecule Polar molecule: opposite charges on opposite ends Weak electrical attractions
Hydrogen bond Water molecules are electrically attracted to oppositely charged regions on neighboring molecules Because the positively charged region is always a hydrogen atom, the bond is called a hydrogen bond Hydrogen bonds are weak bonds important in the chemistry of life
TypeChemical basisStrengthExample Covalent bondsAtoms share electron pairs StrongHydrocarbons, methane Ionic bondsAtoms donate one or more electrons to other atom of opposite charge ModerateSodium chloride Sodium iodide Hydrogen bondsAtoms with partial negative charge attract hydrogen atoms WeakWater, DNA Chemical bonds and attractive forces
Water resistance to temperature change stabilizes ocean temperatures. Evaporative cooling: when a substance evaporates, the surface of the liquid remaining behind cools down
Water’s hydrogen bonds moderate temperature Because of hydrogen bonding, water has a greater ability to resist temperature change than other liquids. The efficiency of evaporative cooling is affected by humidity.
Water Expands When Frozen Fig 2.15 Fewer molecules than an equal volume of liquid
What is a solution? Example What is a solvent? Example What is an aqueous solution? What is a solute? Example
Ionic bond between Na + and Cl - holds ions together in a solid crystal Dissolve in water: The chloride anion (-) attracts the (+) pole of water The sodium cation (+) attracts the (-) pole of water Dissolved ions cannot re- associate into a solid Water is a polar solvent: A polar molecule has opposite charges on opposite ends
Ion in solution Salt crystal Water is the solvent of life
Fig 2.17 Ionization of Water: Water dissociates hydrogen ions H+ hydroxide ions OH- Bases: release OH - (or accept H + ): decrease [H + ] Sodium Hydroxide Na + & OH - Acids: release H+ (or accept OH-): increase [H+] Hydrochloric acid: HCl H+ & Cl- (in your stomach) The chemistry of life is sensitive to acidic and basic conditions
The pH Scale A pH scale (pH = potential of hydrogen) is used to describe whether a solution is acidic or basic. –pH ranges from 0 (most acidic) to 14 (most basic) –A solution that is neither acidic or basic is neutral (pH = 7)
Acid rain Water reacting with pollutants (SO2, NO) pH 2-3 Normal rain: pH 5.6
Buffers minimize changes in pH Buffers Act as H + reservoirs Take up H + ions when they are abundant, release them when they are scarce. Keep proton concentration steady. A buffer that maintains pH 7: accepts protons if pH is < 7, releases protons if pH is > 7
The Carbonic-Acid-Bicarbonate Buffer in Blood When we exercise, we increase the H + concentration in our blood stream: [H + ] increases Blood pH decreases Our blood contains a buffering system
Chemical reactions make and break bonds, changing the composition of matter You learned that the structure of atoms and molecules determines the way they behave –Remember that atoms combine to form molecules –Hydrogen and oxygen can react to form water 2 H 2 O2O2 2 H 2 O Reactants Product