Atoms: The Building Block of Elements

• Elements are made up of atoms. An atom is the smallest particle of an element that has the properties of that element. Atoms are the basic building blocks of all matter.

Structure of an Atom

• All atoms have the same basic structure. The center of the atom is the nucleus.

• They contain positively charged particles called protons (p+).

• Most nuclei contain particles that have a NEUTRAL charge called neutrons (n0).

Structure of an Atom

• The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e-).

Compounds & Bonding

• A compound is a substance that is composed of two or more different elements that are chemically combined.

Covalent Bonds

• Covalent bonding occurs when electrons are shared between two atoms.

Molecules

• A molecule is a group of atoms that are held together by covalent bonds.

• Each particle involved in the molecule contributes one or more electrons to be shared by the atoms to complete their outer shells.

Ionic Bonds

• An atom can give up one or more of its electrons, resulting in a positively charged ion.

• Another atom can gain additional electrons, resulting in a negatively charged particle.

• The two oppositely charged particles are attracted to one another strongly, which results in an ionic bond.

Mixtures & SolutionsA mixture is a combination of elements in which the individual components retain their own properties. Mixtures can be separated easily by physical means, such as mechanical separation, filtration, distillation, or recrystallization.

Chemical Reactions

• Chemical reactions occur when bonds are broken or formed, causing substances to recombine into different substances.

• All of the different chemical reactions that occur within an organism are referred to as the organism’s metabolism. These reactions break down and build molecules that are important for the functioning of organisms.

Mixtures & Solutions

• A solution is a mixture in which one or more substances are distributed evenly in another substance. In other words, one substance is dissolved in another substance and will not settle out of solution.

Acids & Bases

• An acid is any substance that forms hydrogen ions (H+) in water. Acids have a pH value that is less than 7, which is considered neutral.

• A base is any substance that forms hydroxide ions (OH-) when in water. Bases have a pH greater than 7.

Acids & Bases

• The pH scale is a measure of how acidic or basic something is. The scale goes from 0 to 14 and the numerical value is obtained by taking the log of the hydrogen ion concentration.

Water & Its ImportanceA polar molecule is one in which the electrons are shared, but they are shared unequally. The electrons are located closer to one atom than another, resulting in special properties.

Polar water molecules attract ions as well as other polar molecules. For this reason, water is known as the universal solvent, because most substances will dissolve in water.

Water & Its Importance

• Water atoms attract other water molecules.

• The positively charged hydrogen atom of one water molecule attract the negatively charged oxygen atoms of another molecule.

Water & Its Importance

• Because of its polarity, water has the unique property of being able to creep up thin tubes. Plants in particular take care of this property, called capillary action.

Water & Its Importance• Water has a very high specific

heat relative to most other liquids. This means that a large amount of energy is required to raise the temperature of water by a negligible amount. A large amount of heat energy must be lost to cause the temperature of water to go down. This is very important for cells, which exist in an aqueous environment. This property helps cells maintain homeostasis.

Brownian Motion• In 1827, Scottish scientist Robert

Brown observed pollen grains suspended in water. He noticed that the pollen moved constantly in little jerks, like they were being struck by some invisible object. He found that the same thing happened when he observed particles of dye that weren’t living. Brown was observing evidence of Brownian motion, the random movement of atoms and molecules.

Diffusion• Diffusion is the net

movement of particles from an area of higher concentration to an area of lower concentration. Diffusion is a slow process because it depends on the random movement of atoms and molecules.

• Concentration, temperature, and pressure affect the rate of diffusion.

Diffusion• Concentration of the substances is

the primary controlling factor. The more concentrated substances are, the more rapidly diffusion occurs because there are more collisions between the particles of the substances involved.

• An increase in temperature will increase energy and causes more rapid particle motion.

• Increasing pressure will accelerate particle motion and, therefore, diffusion.

Results of Diffusion• Once two liquids

become evenly distributed, molecules continue to move randomly and collide with one another; however, no further change in concentration will occur.

Dynamic Equilibrium

• The continued random movement of particles with no overall concentration change is called dynamic equilibrium.

Diffusion in Living Systems• The difference in concentration

of a substance across space is called a concentration gradient.

• Because ions and molecules diffuse from an area of higher concentration to lower concentration, they are said to move with the gradient. Diffusion will occur until the concentrations are equal and no further diffusion takes place.

The Structure of Carbohydrates

• A carbohydrate is a biomolecule composed of carbon, hydrogen, and oxygen with a ratio of two hydrogen atoms and one oxygen atom per one carbon atom.– CH2O

The Structure of Lipids

• Lipids are large biomolecules that are made mostly of carbon and hydrogen with a small amount of oxygen.

• Fats, oils, waxes, and steroids are all lipids.

• They are insoluble in water because their molecules are nonpolar and are not attracted to water molecules.

The Structure of Lipids• A fatty acid is a long chain of

carbon and hydrogen. • If each carbon in the chain is

bonded to other carbons by single bonds, the fatty acid is said to ‘saturated’.

• If a double bond is present in the chain, the fatty acid is unsaturated.

• Fatty acids with more than one double bond are called polyunsaturated.

The Structure of LipidsLipids are the major components of the membranes that surround all living cells.

The Structure of Proteins

• Proteins are essential to all life. They provide structure for tissues and organs and carry out cell metabolism. A protein is a large, complex polymer composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. The basic building blocks of proteins are called amino acids. There are about 20 common amino acids that combine in different ways to make literally thousands of proteins.

The Structure of Nucleic Acids

• Nucleic acids are complex biomolecules that store cellular information in the form of a code. Nucleic acids are made up of smaller subunits called nucleotides. Nucleotides consist of carbon, hydrogen, oxygen, nitrogen, and phosphorous atoms arranged in three groups—a nitrogenous base, a simple sugar, and a phosphate group.

The Structure of Nucleic Acids

• The nucleic acid deoxyribonucleic acid (DNA) is the master copy of an organism’s information code.

• The information coded in the DNA contains the instructions used to form all of the organism’s enzymes and structural proteins. Thus, DNA forms the genetic code that determines how an organism looks and acts.