Day 1

Seite 1

Classifying Matter

Matter is anything that has mass and occupies space. It can be it can be divided into groups: pure substances and mixtures.

Classification of matter flowchart

A pure substance has a constant composition: all parts of the substance are the same. This means that their properties also remain constant. In chemistry, pure substances are referred to as chemicals. For example, copper and methyl alcohol are pure substances. Pure substances can be divided further into compounds and elements. Compounds are molecules made up of more than one type of atom, such as H2O or NaCl. Elements are made up of the same kind of atom, such as Ca or Br2.

Mixtures display varying properties as the proportions of the components in the mixture change. Mixtures can be divided into two groups: heterogeneous and homogeneous. In homogeneous mixtures, all parts look the same. For example, tomato ketchup is made up of tomatoes, vinegar, salt and spices, but you can't see these parts individually in the mixture, although with a microscope you could see particles of tomato skin and pepper flakes. In chemistry, homogeneous mixtures are often referred to as solutions. On the other hand, heterogeneous mixtures are made up of parts that can be macroscopically distinguished in the mixture. For example, relish is made up of cucumbers, vinegar, red peppers, mustard seeds and spices. It is possible to see each one of these ingredients in the mixture.

Atoms and Ions

The atom is the smallest particle of a chemical element that can exist on its own, and that retains its characteristic chemical properties. It is made up of three main components. The protons and neutrons form the dense nucleus in the center of the atom. The electrons travel around the nucleus.

An ion is an atom that has lost or gained electrons. A positive ion is called a cation, and a negative ion is called an anion. Thus, when a sodium atom loses an electron (which is a negatively charged particle within the atom) the sodium becomes a cation

The atomic number of an atom corresponds to the number of protons the atom has. For a neutral atom, it is also equal to its number of electrons. The atomic number is represented by the letter Z.

The sum of the number of neutrons and protons in an atom is called the mass number. It is represented by the letter A.

The number of neutrons in a given atom can be calculated using the formula:

Neutrons = mass number – atomic number

= A - Z

Example 1

Iron has an atomic number 26. Its mass number is 56. The number of neutrons it contains is:

Neutrons = mass number – atomic number

= 56 – 26

= 30

Therefore, iron atoms have 30 neutrons.

Isotopes are atoms of an element that have the same number of protons but different numbers of neutrons. Isotopes are named by stating the element's name followed by its mass.

Example 2

The element carbon has 3 isotopes: carbon-12, carbon-13 and carbon-14. Since all carbon atoms have 6 protons, carbon-12 has 6 neutrons, carbon-13 has 7 neutrons and carbon-14 has 8 neutrons.

Seite 2

An important aspect of chemistry is practising safety in the laboratory.

Throughout all schools and workplaces in Canada, standard symbols are used to identify materials that are dangerous or potentially hazardous. These standard symbols are useful because they help all people, regardless of language spoken, to be aware of the safety involved in using and storing a product.

This safety system is called WHMIS: Workplace Hazardous Materials Information System.

WHMIS has produced symbols for workplaces and science laboratories. These symbols are found on the product labels of the containers in which materials are stored.

Each one of the three sections is given a rating from 0 to 4, where 0 represents no danger and 4 represents the highest degree of danger. The bottom section of the label indicates the personal protective equipment that should be worn while using that chemical; a letter is used for this part, and the higher the letter, the more protection is needed.

Along with these symbols, Material Safety Data Sheets (MSDS) are given to the employer to keep in a binder and to be reviewed by employees in training. These sheets are also in school laboratories. They must be easily accessible to all staff and kept up to date, as they list important information about the chemicals used, including:

product information

hazardous ingredients

physical data

fire and explosive data

reactivity data

toxicological data

preventative measures to be taken when using the chemical

first aid procedures

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The Periodic Table of the Elements

In 1869, a Russian chemist named Dmitri Mendeleev came up with a way of organizing the elements that were known at that time. He placed them in order of their atomic weight and then grouped them into rows and columns based on their observed chemical and physical properties. Mendeleev had no idea what atoms were made of or why they behaved as they did, however, he was able to put together the periodic table almost as we know it today. His periodic table had gaps in it since some elements were unknown at the time. Based on the gaps in his table, Mendeleev even succeeded in predicting the existence and properties of several new elements.

The columns on his periodic table are called groups or families, while the rows are called periods.

The periodic table of the elements is a table in which all of the known chemical elements are arranged in order of their number of protons. Elements with similar chemical and physical characteristics are grouped in regions within the table.

The periodic table can be divided into several families, which are shown on the example above. The main families are the alkali metals, alkaline earth metals, transition metals, lanthanides, actinides, halogens, and the rare gases.

Electron Arrangement

Electrons are found travelling around the nucleus in regions called energy levels. An element's row on the periodic table indicates how many energy levels it can have. Electrons with more energy occupy higher energy levels. Also, there is a maximum number of electrons that can be in each energy level. Elements 1 and 2 can have a maximum of 2 electrons in their energy level, while elements 3 to 20 can have up to 8 electrons in the highest energy level.

Valence Electrons

The electrons located in the outermost, or highest, energy level in an atom are called the valence electrons. Their layout determines the chemical element's behaviour. Also, the layout of the valence electrons from elements in a common group is identical; there are more shells as you go down the group but the outer shell structure is identical.

The Activity Series

Although properties for elements within a column in the periodic table are similar, the intensity of these properties differs. This is called the activity series and lists metals in order of decreasing reactivity. In the list below, potassium is the most reactive and gold is the least reactive.

The Activity Series

Potassium

Calcium

Sodium

Magnesium

Aluminum

Zinc

Iron

Cobalt

Nickel

Tin

Lead

----------------

Hydrogen

----------------

Copper

Mercury

Silver

Platinum

Gold

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Trends in the Periodic Table

Elements within a group have the same number and distribution of valence electrons. This gives them similar properties; however, these properties are not identical. Instead, there are variations of these properties within a group. These are called periodic trends.

While there are many trends in the periodic table, the most common are:

Atomic radius is the distance from the center of an atom to its outermost edge.

Ionization energy is the amount of energy needed to remove an electron from an atom.

Electron affinity is the energy change that occurs when an atom gains an electron to form a negative ion.

Electronegativity is a measurement of an atom's ability to attract electrons.