Chemistry

Composition of Matter

• Everything is made of matter• Matter takes up space and has mass• Mass is the measure of the amount of matter in

the substance• Mass & weight are not the same• Weight is the measure of the pull of gravity on an

object• Matter exists as a solid, liquid or gas

Elements

• Elements are pure substances which cannot be broken down.

• All elements are arranged on a chart known as the Periodic Table.

• Four elements, Carbon – C, Hydrogen – H, Oxygen – O and Nitrogen – N make up almost 90% of the mass of living things.

Atoms

• Atoms are the simplest part of an element that keeps all the element’s properties

• Atoms consist of 3 subatomic particles-– Protons- Positive charge (p+), found in the nucleus, and

determine the atomic number of the element• Ex – Carbon has 6 protons so its atomic number is 6

– Neutrons - Neutral charge (n), found in the nucleus and when added to the number of protons, determine the atomic mass of the element.

• Ex – Sodium has 11 protons and 12 neutrons so its atomic mass is 11 + 12 = 23amu

– Electrons – Negative charge (e-), high energy particles that spin around the nucleus in energy levels.

Electrons• Electrons move around the nucleus in

orbitals.• Each orbital can hold up to two electrons• Orbitals are grouped in electron shells• Each electron shell contains a specific

number of orbitals. An electron shell containing a single orbital can hold up to two electrons; a shell with four orbitals can hold up to eight electrons.

• Valence electrons – those in the outermost shell.

Figure 2-3

The highlightedelements are the most abundant elementsfound in organisms

Number of unpaired electrons = valence, also # of bonds that could be created.

Compounds

• Compounds are made of atoms of two or more elements chemically combined.

• Chemical formulas represent a compound and show the kind and number of atoms of each element. H20

• The number and arrangement of electrons in an atom determines if it will combine to form compounds.

• Chemical reactions occur whenever unstable atoms combine to form more stable compounds

• Chemical bonds form between atoms during chemical reactions.

Covalent Bonds

• Form between atoms whenever they share 1 or more pairs of electrons.

Ionic Bonds• Occurs when one atom loses and one atoms gains

an electron.

• Positive ions (cations) have more protons than electrons

• Negative ions (anions) have more electrons than protons

• Ionic Bonds

Hydrogen Bonds

• Hydrogen bonds are covalent bonds that form between hydrogen and an electronegative atom.

Molecular RepresentationsMethane Ammonia Water Oxygen

Molecular formulas:

Structural formulas:

Ball-and-stick models:

Space-filling models:

Properties of Water

• Adhesion – Attraction between molecules of different substances (ex. Water sticking to a glass or capillary action)

• Cohesion – attraction of the same substance (ex. Beads of water)

• Solvent – Things can dissolve in them• Expansion upon freezing – water is less dense as a

solid than a liquid• Stable temperature- water absorbs heat from the air

that is cooler and releases heat to air that is cooler. Much energy is needed to heat water and energy is removed to freeze water.

Water Molecules and Hydrogen Bonding

Water is polar. Hydrogen bonds form between water molecules.

Electrons arepulled towardoxygen

Structure of Water: Liquid and Ice

In ice, water molecules form a crystal lattice. In liquid water, no crystal lattice forms.

Liquid water is denser than ice. As a result,ice floats.

Structure of Water: Liquid and Ice In liquid water, no

crystal lattice forms.

Solutions

• A solution is a uniform mixture of one substance in another

• The solute is the substance uniformly dissolved in the solution

• The solvent is the substance in which the solute is dissolved.

• Water is the universal solvent

Acids and Bases

• The force of attraction between molecules is so strong that the oxygen atom of one molecule can actually remove the hydrogen from other water molecules; called dissociation. H2O ----goes to --- H+ + OH-

• OH- called hydroxide ion • H+ called hydrogen ion

• Acidity or alkalinity is a measure of the relative amount of H+ and OH- ions dissolved in a solution.

Acids and Bases Defined

• Neutral solutions have an equal number of H+ and OH- ions dissolved in a solution

• Acids have form H+ ions than OH – ions; taste sour and can be corrosive

• Bases contain more OH-ions than H+ ions, taste bitter; and feel slippery

• Buffers neutralize acids or bases to help maintain homeostasis.

• 0 - 14 scale

• 0 - 6.9 Acidic• 7 Neutral• 7.1-14 Basic