Chemistry Basics

Objectives:• Differentiate between atoms, elements, ions, molecules, *isotopes,

and *isomers (*not in book, use notes or other resource) • Distinguish between covalent, ionic, and hydrogen bonds• Differentiate between: solvent and solute, acid and base, cohesion

and adhesion and capillary action• Describe what influences pH and how it affects life.• Elaborate on water’s qualities and why it is essential to life.

Vocabulary Words:Atom * Element * Ion * Molecule * Isotope * IsomerCovalent Bond * Ionic Bond * Hydrogen Bond * Solute * Solvent Capillary Action * Acid * Base * buffer * alkaline * Adhesion Cohesion * Hydrophilic * hydrophobic * polar molecules * hydroxide ion * hydronium * heat capacity

Know answers for p. 50, numbers 5, 6, 8, 10, 11

Everything is made of atoms:

Atoms are made of:

•Nucleus

•Neutrons – No Charge, mass of approx. 1 amu

•Protons – (+1) Charge per proton, mass of 1 amu

•An Outer “Electron Cloud”

•Electrons – have a (-1) charge and relatively no mass. They circle the nucleus in a region often referred to as an electron cloud. They are found in energy levels called orbitals. Hydrogen and helium have only one orbital that will fit only 2 electrons. The next series of elements (atoms) can hold 8 electrons. Larger atoms can hold more electrons in their outer orbital. The number of electrons in the outer orbital (valence electrons) determines much of the atoms attraction, or bonding ability, to other atoms.

An atom has no electrical charge.

Element - a substance that can’t be broken down into any other substance by chemical means. These are arranged in the “Periodic Table” in groups (the columns) and periods (the rows).

Groups list elements with similar properties such as reactivity and charge.

Periods will increase in number of protons from left to right.

The periodic table also lists each element by its chemical symbol, atomic number, and atomic mass.

Ions - are atoms that have either lost or gained electrons and are now charged.

Isotopes – are atoms with the same number of protons but vary by their number of neutrons. Ex: Carbon 12 and Carbon 14. Tin (Sn) has the greatest number of isotopes with 10 !

Chemical formulas use chemical symbols and subscripts to show what elements are present in a compound (cluster of joined atoms). For example C2H6O

Isomers - compounds with the same chemical formula but different structure, or location of atoms in the bonding sequence.

H H H H

H - C - C - O - H H - C – O – C – H

H H H H Ethyl alcohol dimethyl ether

These isomers will have different chemical properties.

Isomers can be cis- or trans- forms. These can sometimes act as on/off switches in living organisms.

Cl Cl Cl H

C = C C = C

H H H Cl Cis – 1,2 – dichloroethane Trans – 1, 2, - dichloroethane

(“boat”) (“chair”)

This is NOT a cis-/trans- isomer: Cl and H can’t switch to a

Cl H different Carbon C = C

Cl H

Chemical Bonds

What determines the type of bond? This is partly determined by the number of valence (outer) electrons and the electronegativity (pull) of the elements involved.

Covalent bonds – tend to form between atoms with 3 to 5 valence electrons (Ex: carbon). Electrons are shared between atoms. Atoms held together by covalent bonds are called molecules. Carbon, nitrogen, oxygen, and hydrogen readily form covalent bonds

Ionic Bonds – tend to form between atoms with 1 or 2 (occasionally 3) valence electrons and atoms with 5, 6, or 7 valence electrons. The element with 5 to 7 valence electrons “steals” the electrons from the element with 1 to 3 valence electrons. This makes the first element negatively charged (gained electrons) and the atom losing 1 to 3 electrons is now positively charged. The opposite charges attract.

Covalent bonds are strong. Most of the major components of living organisms, such as fats, proteins, and carbohydrates, are held together by strong covalent bonds.

Ionic bonds tend to break in water and allow the ions to dissociate. Ex: NaCl in water becomes Na+ and Cl -. Most of the essential minerals (metals) of life are ionically bound to other elements but these bonds disassociate in water so K+, Na+, Mg++, etc. can be utilized by our cells.

Hydrogen bonds are also important to life. In fact, these hold the 2 DNA strands together in a double helix. Individually, these are weak bonds, but with many working together, they are strong. Hydrogen bonds link molecules, not individual atoms, together. In order for hydrogen bonds to form, the molecules must be close together (due to the weak pull). It is hydrogen bonds that allow water to be a liquid on Earth. Our atmosphere is mostly N2 and O2 , but H2O is much lighter than these molecules so individual H2O molecules “float” in air as water vapor. Only when linked together, by hydrogen bonds, are they heavy enough to “sink” and form liquid water.

Water is a polar molecule. Polar molecules have unequal charge distribution. The oxygen atom pulls harder for the electrons than the hydrogen atoms do. This gives the oxygen area a slightly negative charge and the hydrogens a slight positive charge. This is what allows water molecules to form hydrogen bonds between molecules. Cohesion is the term used for the attraction between water molecules. Adhesion is the term used for water’s tendency to cling to other polar surfaces, like glass. This can cause a meniscus to form or water to climb up the surface. When water is drawn high up along a surface, it’s called capillary action.

Water is essential to life. Hydrophilic (hydro – water, philic – loving) substances are attracted to water. Hydrophobic (phobic – fearing) substances are repelled by water. Our cell membranes have both hydrophilic and hydrophobic layers that help control what substances get in and how they do it.

About two-thirds of the molecules in our bodies are water molecules. Water is an excellent solvent. Solvents dissolve other substances, called solutes. Ex: Salt dissolves in water. Water is the solvent, salt is the solute. It is “soluble.” Covalently bonded molecules, such as sugar, stay as individual molecules dispersed between water molecules. Ionically bonded compounds like salt (NaCl), separate into their component ions: Na+ and CL-, in this case.

Water itself can ionize into OH- (hydroxide ions) and H+ ions which join with water molecules to form hydronium ions (H3O+). These balance each other when only water is involved. And, only about 1 of 550 million water molecules ionize in pure water. However, other compounds containing hydrogen sometimes readily form hydronium ions. Hydrogen ions, or hydronium ions, dissolved in water, when not balanced by hydroxide, create an acid. If a compound dissolved in water forms an excess of hydroxide ions, it is a base, or an alkaline solution.

A solution’s acidity is measured on the pH scale. This is a negative log rhythmic scale. In other words, a pH of “6” means the concentration of hydronium ions is 10- 6 ( .000001). A pH of “7” is neutral. Anything below “7” is acidic (more hydronium ions), anything above “7” (fewer hydronium ions) is basic, or “alkaline”. The pH scale ranges from 0 to 14. Each numerical increment is a multiple of ten (log rhythmic scale) above or below the next consecutive number. For example, a pH of “3” (.001) means there are 10x more H+ ions than a pH of “4” (.0001). So, the lower the pH, the more acidic.

Our stomach has an acidic pH but our intestines are alkaline. Our blood is normally between 7.35 and 7.45. A blood pH below 7.0 (severe acidosis) or above 7.8 (severe alkalosis) is deadly. Buffers help regulate pH by either donating or accepting H+ ions.

One human body buffer system relies on the following reactions:

HCl + NaHCO3 H2CO3 + NaCl(strong acid) (weak acid)

NaOH + H2CO3 NaHCO3 + H2O(strong base) (weak base)

Another important feature of water is its heat capacity. Water is very slow to gain or lose heat. This helps living organisms maintain a more steady body temperature.

Water is also unique because it becomes LESS dense when it forms a solid. Water is at its most dense at about 4 degrees Celsius. So, ice floats. This adds a layer of insulation over ponds and lakes and helps to prevent freezing all the way from the bottom up as would happen with other substances. Without this unique quality, ponds and lakes in the northern parts of the US would not support fish or other animal life through cold winters.