Chemistry of life

Everything-whether it is a rock, frog, or flower-is made of substances called elements.An Element is a substance that can’t be broken down into simpler chemical substances.Of all the elements, only about 25% are essential to living organisms.Carbon, hydrogen, oxygen, and nitrogen together make up more than 96% of the mass of a human body.

• Trace elements such as iron and copper are present in living things in very small amounts. They play a vital role in maintaining healthy cells in all organism.

Atoms: The building blocks of Elements• An atom is the smallest particle of an element

that has the characteristics of that element.• Atoms are the basic building blocks of all

matter.

The structure of an atom

• The center of an atom is called the nucleus• All nuclei contain positively charged particles

called protons. p+• Particles that have no charge are neutrons. n0• All nuclei is positively charged• Each element has a different number of

protons.

• The element iron differs from element aluminum because iron atoms have a different number of protons than aluminum atoms.

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

• How are electrons held in this region? The electrons are held in this region by their attraction to the positively charged nucleus

Electron energy levels

• Electrons exist around the nucleus in regions known as energy levels.

• The 1st energy level can hold 2 e-`• The 2nd energy level can hold 8 e-• The 3rd energy level can hold up to 18 e-Atoms contain equal numbers of electrons and protons, therefore, they have no net charge.

Isotopes of an Element

• Atoms of the same element always have the same number of protons but may contain different numbers of neutrons.

• Atoms of the same element that have different numbers of neutrons are called isotopes.

• Example the most common atom is referred to as carbon-12 because it has 6 protons and 6 neutrons. Other isotopes of carbon include carbon-13 and carbon-14.

Compounds and Bonding

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

• Table salt (NaCl) is a compound composed of elements sodium and chorine.

• Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms.

Compounds and Bonding

• An atom becomes stable when its outer most energy level is full, as when eight electrons are in the second level.

• Exception is hydrogen, which becomes stable when its first energy level is full.

Compounds and bonding

• Each atom becomes stable by sharing its electron with the other atom.

• The attraction of the positively charged nuclei for the shared, negatively charged electrons holds the atoms together.

• When 2 atoms share electrons, such as two hydrogen atoms sharing electrons, that force that holds them together is called covalent bond.

Compounds and Bonding

• Most compounds in organisms have covalent bonds. Example include sugars, fats, proteins, and water.

• A molecule is a group of atoms held together by covalent bonds. It has no overall charge.

Quiz

1. An _________is a substance that can’t be broken down into simpler chemical substances.

2. ___________ are the basic building blocks of all matter.3. What 4 elements make up 96% of the human body?4. What are atoms composed of?5. These elements that are present in living things in very small amounts and play a vital role in maintaining healthy cells in all organism are called______?

Ionic Bonds

• Not all atoms bond with each other by sharing electrons.

• Sometimes atoms combine with each other by first gaining or losing electrons in their energy levels.

• An atom that gains or loses electrons has an electrical charge and is called an ion.

• An ion is a charged particle.

• Ex. NA+, K+, Cl-Ionic bonds is a different type of chemical bond holds ions together.

Sodium (Na) has 11 electrons and chlorine atom has 17 electrons.

So the way that NA and Cl bond is by Na losing an electron and Cl gaining an electron.

When you lose an electron you get a positive net charge. When you gain an electron you get a negative charge.A positively charge ion is called a cation and a negatively charge ion is called a anion.

• The attractive fore between two ions of opposite charge is known as an ionic bond.

• Ionic compounds are less abundant in living things than are covalent molecules, but ions are important in biological process.

• Ex. Sodium and potassium ions are required for transmission of nerve impulses. Calcium ions are necessary for muscles to contract. Plant roots absorb essential minerals in the form of ions.

Chemical Reactions

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

• In organisms, chemical reactions occur inside cells• All of the chemical reactions that occur within an

organism are referred to as that organism’s metabolism.

• These reactions break down and build molecules that are important for the functioning of organisms.

Acids and Bases

• Chemical reactions can occur only when conditions are right.

• A reaction may depend on available energy, temperature, or a certain concentration of a substance dissolved in solution.

• Chemical reactions in organisms also depend on the pH of the environment within the organism.

Acids and bases

• The pH is a measure of how acidic or basic a solution is.

• A scale with values ranging from below 0 to 14 is used measure pH.

Acid and Bases• A neutral pH is 7 meaning it is not an acidic or

basic. Ex. Distilled water.• A substances with a pH below 7 are acidic.

Acids have Hydrogen ions (H+). The more acidic the substance the higher the concentration of H+.

• A substances with a pH above 7 are basic. Bases have hydroxide ions (OH-). The more basic the substance the higher the concentration of OH-.

Acid and bases• Many of the foods you eat, such as oranges

and grapefruits are acidic. • Some plants grow well only in acidic soil,

whereas others require soil that is basic. • Acids and bases are important to living

systems, but strong acids and bases can be dangerous.