All Matter Consists of Elements Chemistry is the study of matter Matter is – Anything that has mass and occupies space – Composed of elements Elements – Cannot be broken down to a simpler form – Periodic table of elements – lists all known elements

Figure 2.2 Group number Atomic number Element symbol Atomic mass Nonmetals Metals Transition elements Lanthanides Actinides Metals Non metals

Atoms – Smallest Functional Unit of Elements Atoms consist of – Nucleus (central core) Protons – positive charge – have mass Neutrons – no charge – have mass – Shells (surrounding nucleus) Electrons – negative charge – no discernable mass

Figure 2.3 Electron Proton Shell Neutron Nucleus a) Hydrogen 1 proton b) Oxygen 8 protons 8 neutrons 8 electrons in 2 shells c) Sodium 11 protons 11 neutrons 11 electrons in 3 shells

More About Atoms Atomic symbol: one or two letters – Na: sodium – O: oxygen Atomic number – Number of protons Atomic mass – Roughly equal to number of protons plus neutrons In an electrically neutral atom – Number of protons = number of electrons

Isotopes Have a Different Number of Neutrons Same atomic number (same number of protons) Different atomic mass (different number of neutrons) Unstable isotopes are called radioisotopes Radioisotopes give off – Energy (in the form of radiation) – Particles

Unstable isotopes are called radioisotopes – Give off energy in the form of radiation Some radioisotopes have scientific and medical uses – Carbon-14: used for dating fossils – Diagnostic imaging – Cancer treatment – Power supply for implants such as cardiac pacemakers Isotopes Have a Different Number of Neutrons

Energy Fuels Life’s Activities Energy: the capacity to do work Potential energy: stored energy Kinetic energy: energy in motion, doing work Potential energy can be transformed into kinetic energy

Energy Fuels Life’s Activities Electrons have potential energy – Each shell corresponds to a specific level of potential energy – Shells that are farther from the nucleus contain electrons with more potential energy Atoms are most stable when their outermost shell is full Atoms will interact with other atoms to fill their outermost shells

Chemical Bonds Link Atoms to Form Molecules Chemical bonds: attractive forces holding atoms together Kinds of chemical bonds – Covalent bonds – Ionic bonds – Hydrogen bonds

Covalent Bonds Covalent bonds form when atoms share electrons Very strong bonds Examples – Hydrogen molecule: H 2 – Oxygen molecule: O 2 – Water: H 2 O

Figure 2.5 Written formula Structural representation Structural formula with covalent bond Hydrogen (H 2 ) Oxygen (O 2 ) Water (H 2 O) Two single covalent bonds Single covalent bond Double covalent bond

Covalent Bonds Nonpolar covalent bonds: electrons are shared equally – H 2 – O 2 – CH 4 Polar covalent bonds: electrons are NOT shared equally – H 2 O: The oxygen has a stronger pull on the shared electrons than the hydrogen does

Ionic Bonds Ion: an electrically charged atom or molecule Positively charged ion: forms if an atom or molecule loses electrons Negatively charged ion: forms if an atom or molecule gains electrons Ionic bond: attractive force between oppositely charged ions Example: NaCl

Figure 2.6 Loss of electron: positive charge Gain of electron: negative charge Sodium atom (Na)Chlorine atom (Cl)Sodium ion (Na + ) Sodium chloride molecule (NaCl) Chloride ion (Cl – )

Hydrogen Bonds Form between polar molecules Polar molecules – Contain polar covalent bonds in which there is unequal sharing of electrons – Electrically neutral overall, but uneven charge distribution Hydrogen bond – Weak attraction between oppositely charged regions of polar molecules – Example: weak forces between water molecules

Figure 2.7 Molecule Oxygen (O) Hydrogen (H) Water Ice

Life Depends on Water Water molecules are polar Water is liquid at body temperature Water is the biological solvent Water can absorb and hold heat energy Water helps regulate body temperature

Water Is the Biological Solvent Solvent: liquid in which other substances dissolve Solute: any dissolved substance Hydrophilic: polar molecules that are attracted to water and interact easily with water Hydrophobic: nonpolar neutral molecules that do not interact with or dissolve in water

Figure 2.8 Ions in solution Molecules of water Salt crystal

The Importance of Hydrogen Ions Acids: – Donate hydrogen ions (protons) – Increase hydrogen ion concentration in solutions Bases – Accept hydrogen ions (protons) – Lower hydrogen ion concentration in solutions pH Scale – A measure of hydrogen ion concentration

The pH Scale Measure of hydrogen ion concentration in solution Ranges from 0 to 14 – Acids: pH < 7 – Neutral: pH = 7 – Basic: pH > 7

pH values Concentrations of H + (moles/liter) Drain opener Bleach Ammonia cleanser Soapy water Baking soda Human blood, tears Saliva, urine Black coffee Tomatoes Vinegar, cola Lemon juice Hydrochloric acid Concentrated nitric acid More acidic Neutral pH More alkaline –13 10 –11 10 –9 10 –7 10 –5 10 –3 10 –1 0 Figure 2.10

Buffers Minimize pH change Help maintain stable pH in body fluids Carbonic acid and bicarbonate act as one of the body’s most important buffer pairs HCO H + H 2 CO 3

Water and Chemistry