Lecture 3

Question 2

Element

Answer 2

A chemical element is the simplest form of matter to have unique properties Each element is identified by an atomic number, the number of protons in its nucleus i.e. Water has unique properties but it can be broken down into two elements, H and O that have unique properties of their own

Question 3

Protons, neutrons and electrons

Answer 3

Protons have a single positive charge; weighs approximately 1amu Neutrons have no charge; weighs approximately 1amu Electrons have a single negative charfe and very low mass (1836 electrons = 1amu)

Question 4

Isotopes and radioactivity

Answer 4

Isotopes are elements that differ from one another only in number of neutrons and therefore in atomic mass

• Although different isotopes of an element exhibit identical chemical behavior, they differ in physical behavior, many are unstable and decay to more stable isotops by giving off radiation i.e. 1H (Hydrogen), 2H (Deuterium) and 3H (Tritium) Radioactivity the process of decay of unstable isotopes (radioisotopes)
• Each radioisotope has a characteristic physical half life, the time required for 50% of its atoms to decay to a more stable state

Question 5

Ions

Answer 5

Ions are charged particles with unequal numbers of protons and electron An ion can consist of a single atom with a positive or negative charge or it can be as large as a protein with many charges on it Ions form because elements with 1-3 valence electrons tend to give them up and those with 4-7 electrons tend to gain more Ionization -the process when an atom transfers electsons from one to another and turn both of them into ions

Question 6

Ions - anion

Answer 6

Anion - the particle that gains electrons acquires a negative charge

Question 7

Ions - cation

Answer 7

Cation - the particle that loses electrons acquires a positive charge (because it then has a surplus of protons)

Question 8

Chemical bonds

Answer 8

Covalent Ionic Hydrogen Van der Waals forces

Question 9

Chemical bonds - Covalent

Answer 9

• Sharing of one or more pairs of electrons between nuclei Nonpolar covalent bond- the strongest of all chemical bonds; when shared electrons spend approximately equal time around each nucleus Polar covalent bond- If shared electrons spend significantly more time orbiting one nucleus than they do the other, they lend their negative charge to the region where they spend the most time i.e. H-O, electrons are more attracted to the O and makes that region of the molecule slightly negative and the H region slightly positive

Question 10

Chemical bonds - Ionic

Answer 10

Is the attraction of a cation to an anion, but no sharing of electrons i.e. Sodium (NA+) and Chloride (Cl-) ions are attracted to each other and form the compound sodium chloride (NaCl)

Question 11

Chemical bonds - Hydrogen

Answer 11

• A Weak attraction between a slightly positive H atom in one molecule and a slightly negative O or N atom in another
• H bonds also form between different regions of the same molecule, esp in very large molecules such as protein and DNA; they cause such molecules to fold or coil into precise 3D shapes i.e. H2O are weakly attracted to each other by H bonds

Question 12

Chemical bonds - Van der Waal forces

Answer 12

• Are weak, brief attractions netween neutral atoms
• Oppositely charged regions of two atoms attract each other for a very short instant in time
• A single van der Waals forces is only about 1% as strong as a covalent bond, but when two surfaces or large molecule meet, they van der Waal forces between large numbers of atoms can create a strong attraction i.e. plastic wrap clings to food and dishes; a gecko can run up a windowpane