Chapter 2: The Chemistry Of Life

Atoms: What is an atom? –The basic unit of matter Incredibly small: 100,000,000 atoms lined up in a row would only be the width of your pinky finger! But there are even smaller particles that make up atoms.

Subatomic Particles Three types: Protons, Neutrons, Electrons Protons: –Positively charged Neutrons: –Neutral in charge Electrons: –Negatively charged particles –are about th the size of a proton or neutron.

Subatomic particles Cont’d. Protons and neutrons have about the same mass. Nucleus: located at the center of the atom and is made up of protons and neutrons. Electrons are in constant motion and surround the nucleus like a cloud –They are attracted to the positive nucleus but are not part of the nucleus because they are in constant motion

Atoms have equal numbers of protons and electrons so they are neutral in charge.

What is a Chemical Element? A chemical element is a pure substance that is made entirely out of one type of atom. Elements are represented by a one or two letter symbol. –Ex: C is the symbol for carbon. –Pb is the symbol for lead.

Elements and Isotopes The number of protons in an element is that element’s atomic number. Atoms of an element can have different numbers of neutrons. Example: some atoms of carbon have 6 neutrons and some have seven –These are called isotopes Isotopes occur when atoms of the same element have a different number of neutrons Radioactive isotopes: meaning their nuclei are unstable and break down at a constant rate over time.

Let’s look at some examples of Isotopes Red = protons Green = neutrons

In nature, most elements are found combined with other elements in a compound. What is a compound? A compound is a substance that is formed by the chemical combination of 2 or more elements in definite proportions. –Ex: H 2 0 contains 2 atoms of Hydrogen and one atom of Oxygen. Chemical Compounds

Chemical Bonds Atoms in compounds are held together by chemical bonds. Chemical bond Atom 2 Atom 1

Ionic Bonding Ionic bonds are formed when one or more electrons are transferred from one atom to the other Let’s look at an example: Positively and negatively charged atoms are known as ions. Na+ + Cl- NaCl

Ionic Bonds Cont’d Remember that atoms are electrically neutral because they have equal numbers of protons and electrons An atom that loses electrons has a positive (+) charge, and an atom that gains electrons has a negative (-) charge Ionic Bonding video

Covalent Bonding Sometimes electrons are shared by atoms instead of being transferred Covalent bonding occurs when electrons are shared between atoms When the atoms share two electrons it is called a single covalent bond:

Covalent Bonding Cont’d When they share 4 electrons it is called a double covalent bond: And if they share 6 electrons it is called a triple covalent bond: Covalent bonding video

The structure that results when atoms are joined together by a covalent bond is called a molecule. What does it all mean?

Section 2-2: Properties of the Water Molecule Water molecules, like all molecules, are neutral. The water molecule is known as a polar molecule What does this mean? It is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.

Water Water molecules are held together by Hydrogen Bonds which are the weakest type of bonds This ability to form multiple hydrogen bonds is responsible for many of water’s properties.

Cohesion Cohesion is an attraction between molecules of the same substance. Cohesion causes the molecules on the surface of water to be drawn inward, which is why drops of water form beads on a smooth surface and why some insects can float on top of water.

Other properties of water Adhesion is an attraction between molecules of different substances. Adhesion between water and glass causes water to rise in a narrow tube against the force of gravity. –This effect is called capillary action.

Solutions and Suspensions Water is not always pure. It is often found as part of a mixture. What is a mixture? –A Mixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. Ex: salt and pepper

Two types of water mixtures Solutions: mixtures of two or more substances in which the molecules of the substances are evenly distributed –Ex: salt mixed into warm water What are some other examples of solutions?

Solutions Cont’d. The salt is he solute, or the substance that is dissolved The water is the solvent, or the substance that dissolves the solute. What are the solutes/solvents in your examples?

Suspensions Suspensions are mixtures of water and non-dissolved materials –Ex: blood in your body