Introduction to Some Chemistry IdeasUnderstanding chemistry…

Would you ban the following compound – Dihydrogen monoxoide (also called hydric acid)?•It is a colourless, odourless chemical compound•It is a highly reactive radical•is a key ingredient in most pesticides•It can mutate DNA, denature proteins, disrupt cell membranes and chemically alter critical neurotransmitters•It contributes significantly to many environmental problems such as acid rain and soil erosion, and it contributes to the Earth’s Greenhouse Effect•It is used in vast quantities by every industry on Earth•It is partially responsible for the spread of pollutants present in contaminated rivers, lakes and oceans•In its gas state, it can produce painful burns to exposed skin•Its atomic components are found in many caustic explosives and poisonous compounds such as sulfuric acid, nitroglycerine and ethyl alcohol•It can cause severe illness or death in either very low or very high concentrations•It is legally discarded as waste be individuals, businesses and industries•It can cause death if inhaled (…even in very small quantities)•If there is prolonged exposure to its solid state, it can cause severe tissue damage•It decreases the effectiveness of automobile brakes•It contributes to corrosion and oxidation of many metals

Introduction to Some Chemistry Ideas

Chemistry•The study of matter AND how it reacts or combines when different forms and types of matter come together.•A physical science that deals with the composition, structure and properties of substances and the reactions they undergo

Introduction to Some Chemistry Ideas

MatterAnything that has mass and volume.

Mass is the amount of matter a substance contains. NOTE: Mass and weight are different. Weight is due to gravitational pull

Volume is the amount of space that an object takes up

Introduction to Some Chemistry Ideas

Physical Change•Affects physical appearance of the substance BUT not the substance’s composition. That is, the MATTER of the substance is not altered.

Chemical Change•Alters the composition of the matter (e.g., decomposing water using electrical energy – 2H2O 2H2 + O2

Introduction to Some Chemistry Ideas

Mixture•Physical combination of two or more kinds of matter. NOTE: It is not chemical bonding.•Two types: Homogeneous and Heterogeneous. Homo is Greek for “same” while Hetero is Greek for “different”

Introduction to Some Chemistry Ideas

Pure Substance•Delimited composition that is retained in response to physical change.•Two types: Element and Compound. An element cannot be separated into a simpler substance. A compound is two or more elements that combine CHEMICALLY in a set ratio to form a different substance AND you are able to break it down into elements using chemical processes

Introduction to Some Chemistry Ideas

Atom•The smallest particle of an element that retains the identity and properties of the element.•Atoms consist of three subatomic particles: (1) protons, (2) neutrons and (3) electrons

Introduction to Some Chemistry Ideas

Proton•Positive charge•Mass of 1. In grams, proton mass is 1.67 X 10-24g•Located in nucleus

Neutron•No charge (neutral)•Mass of 1. In grams, neutron mass is 1.67 X 10-24g•Located in nucleus

Electron•Negative charge•So small, mass is considered to be 0. In grams, electron mass is 9.02 X 10-28g•Located in shells or orbits located around the nucleus•Moving

Introduction to Some Chemistry Ideas

Considering the mass of neutrons and protons (1.67 X 10-24g), there must be 602,000,000,000,000,000,000,000 neutrons and protons (…or 6.02 X 1023) in 1g.

In chemistry, this is a VERY IMPORTANT number: 6.02 X 1023 is Avogadro’s Number (…after the person who measured it). It is the number of atoms per mole of a given substance. A mole is a unit of measurement to express amounts (…rather than mass or volume).

Thinking it through – 1 / 6.02 X 1023 = 1.67 X 10-24 which is called Atomic Mass Unit (u). 1u = 1.67 X 10-24g

Introduction to Some Chemistry Ideas

This represents the element Helium.

The Atomic Symbol is He

The Atomic Number is 2. That is the number of protons (…and electrons)

The Atomic Mass is 4. It is the number of protons + the number of neutrons. Helium has 2 protons. Thus, helium has 2 neutrons (4 – 2 = 2)

Introduction to Some Chemistry IdeasIsotopeAtoms of an element that have the same number of protons BUT a different number of neutrons.

The diagram shows three isotopes of hydrogen: protium (no neutrons), deuterium (1 neutron) and tritium (2 neutrons).

Since neutrons has no electrical charge, the chemistry of the element is not impacted. However, the mass of the element changes.

Isotopes can be stable or unstable. Unstable isotopes decay. They are radioactive. NOTE: All anthropogenic elements are radioactive isotopes.

Introduction to Some Chemistry IdeasNoble Gases

The Noble Gases are elements that have a stable electron configuration (i.e., their outer shell of electrons if full – called a Stable Octet).

Because they are stable, Noble Gases are non-reactive (i.e., they do not form compounds naturally).

Noble Gases exist as individual atoms in nature. Most of the other elements cannot exist as individuals. Metals that CAN are gold, silver and platinum.

Introduction to Some Chemistry Ideas

Trends in the Periodic Table

One trend is Atomic Radius.

As shown, the size of the atom increases, as expected, as you move down a column (called Family or Group). Unexpectedly, atomic radius decreases as you move across a row (called a Period). Why?

Introduction to Some Chemistry IdeasTrends in the Periodic Table

Other aspects include •Ionization Energy – amount of energy required to remove an electron from a gaseous atom or ion•Electron Affinity – measure of the change in energy that occurs after an electron is added•Electronegativity – measure of an atom’s ability to attract electrons in a chemical reaction

These three aspects all increase as you move UP a Family and across left-to-right a Period. Why?

Introduction to Some Chemistry Ideas

Elements are neutral. That is, the number of positively-charged protons is the same as the number of negatively-charged electrons (p+ = e-) so the overall charge is zero.

In an ionic chemical bond, some elements give or take electrons to become an ION. If a non-metal adds a negative charge (i.e., takes an electron), the ion becomes negatively-charged. It is called an ANION. If a metal gives away a negative charge (i.e., gives an electron), the ion is positively-charged. It is called an CATION.

Introduction to Some Chemistry Ideas

Chemical BondsThere are three types of chemical bonds: (1) ionic, (2) covalent (polar or non-polar) and (3) metallic.

The difference in electronegativity between the elements determines the TYPE of chemical bond that will occur.– ΔEN between 1.7 and 3.3 forms an ionic

bond– ΔEN between 0.5 and 1.7 forms a polar

covalent bond– ΔEN is between 0 and 0.5 forms a non-

polar covalent bond

Introduction to Some Chemistry IdeasChemical BondsAn ionic bond occurs when ions give-and-take electrons.

A covalent bond occurs when electrons are shared. A non-polar covalent bond occurs when the electron is shared equally between; whereas, a polar covalent bond occurs when the electron is not shared equally. In a polar situation, one element has a negative charge while the other element is positive