Pure substances and the Periodic table Lesson 11

Pure substances Water is a pure substance. When electricity is passed through it, it separates into Hydrogen and Oxygen gas. This is known as the electrolysis of water.

What happens as the electricity passes though the water? The electricity splits the compound into its two elements, hydrogen and oxygen.

Chemical Tests Chemical changes can be useful ways for us to determine what unknown substances we are dealing with. Here are 4 tests that can be done to test for common for 4 different gasses commonly found in the lab.

Chemical Tests Oxygen Gas If a glowing splint bursts into flames when placed in the gas. The more concentrated oxygen in the test tube makes the combustion happen faster.

Chemical Tests Hydrogen gas Is indicated if a flaming splint at the mouth of the test tube causes a “pop” or small explosion in the gas. Hydrogen is highly flammable.

Chemical Tests Carbon dioxide gas is indicated if limewater solution turns milky when the gas is bubbled into it. The limewater undergoes a chemical change to for an insoluble white precipitate. Or A flaming splint at the mouth of the test tube is extinguished

Chemical Tests Water vapour is indicated if cobalt chloride test paper changes from blue to pink.

Elements When water was split into two parts, it was divided into two elements. Elements are the most pure kind of substances. You cannot split them into anything simpler. Elements have only one kind of Atom. Atom is a word that the ancient Greeks developed. It means “the smallest particle of matter, which cannot be divided.”

Atom Structure Atoms are composed of three subatomic particles Protons- Heavy positively charged particles found in the nucleus Neutrons -are neutral particles that have the same mass as protons and are located in the nucleus Electrons- Negatively charged particles with almost no mass. They circle the nucleus at different energy levels.

nucleus

The short form for water is H2O because water is made of two elements, oxygen and hydrogen. H is the short form for hydrogen. O is the short form for oxygen

The chemical formula H2O is known as a Molecule The chemical formula H2O is known as a Molecule. A molecule is a combination of atoms. It is the smallest part of a compound. The 2 in H2O means that there are 2 hydrogen atoms in the molecule.

Compounds Compounds are made by combing two or more different elements. Example: sodium chloride is made up of sodium metal and chlorine gas. These elements combine to make table salt.

+  Chlorine is a poisonous greenish gas. Sodium is a silvery metal that explodes in water.  Sodium Chloride is a white crystal that is good to eat. Element Compound

Each Compound has only one kind of molecule Each Compound has only one kind of molecule. The atoms that are combined to make the molecules are bonded together. This means that they cannot come apart without a chemical reaction. Ended here

Are the properties of sodium chloride different from the properties of sodium and chlorine? Explain. The properties are very different. The elements are potentialy dangerous while the compound is safe to eat.

The Periodic Table of the elements Symbols are pictures or letters that stand for something else. Chemists use one or two letters as symbols represent elements. The symbols for the elements are the same all over the world. Example: The symbol for oxygen is O. The symbol for chlorine is Cl. Look at the periodic table for more examples.

Chemists organize the elements in a chart called the periodic table Chemists organize the elements in a chart called the periodic table. Each element has a number, and the elements are arranged in order in the chart.

Atomic Number Z Element Name Element Symbol Atomic Mass A

Elements are classified by their state at room temperature Elements are classified by their state at room temperature. Most elements are solid at room temperature. Some are gases. Only mercury (Hg) and bromine (Br2) are liquid at room temperature.

Metals, Non-metals, and Metalloids Another way elements can be classified is into metals, non-metals, and metalloids. Metals Good conductors of heat They can be shaped easily They are shiny, and they are usually solid. Colour green

Non-metals Poor conductors of heat They are brittle They are not shiny They are usually solids or gases They are in the top right corner of the table Colour Orange

Metalloids - Have some properties of metals and some properties of non-metals. -They are found on the table along the staircase line that separates metals from non-metals -Colour blue

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