Chapter 4 Compounds and Mixtures

Matter is sorted just like you would sort things in your life. Matter is divided into 3 groups. Elements: made of only one kind of atom. Compounds: made up of atoms of two or more elements that are chemically combined. The elements are combined in a mixed ratio. Example: Salt is made up of 1 atom of sodium and 1 atom of chlorine.

Mixture: made of two or more kinds of matter that are physically combined or mixed together. There can be any amount of matter in the mixture. Example: Salad, sugar and cinnamon, salt and sugar.

Elements and Compounds have similar characteristics. If you have a sample of an element, another sample of the exact same element has the exact same properties. Same with a compounds. If you have a sample of a certain compound, the exact same compound in a different sample will have the exact same properties. Examples: Sugar that you use in your cookies when you bake is the same sugar that makes up candy.

Because elements and compounds have similar characteristics, they are called substances: any element or compound.

Elements combine with other elements to become compounds. What is a compound? Substance made up of two or more elements that are chemically combined Example: hydrogen and oxygen are both elements that are gases but when they combine they make WATER!!

What are some common compounds?

Properties of compounds are very different then the properties of the elements that make them up. Some elements may be very dangerous but when they combine to make a compound they are not. Example: sodium explodes when added to water. Chlorine is a poisonous gas. When they combine, they make table salt.

Most compounds are made of molecules: the smallest part of a substance that has all the same properties of that substance. It can be made of a single atom or a lot of atoms. Example: Molecule of lead is one atom of lead. A molecule of sucrose is 45 atoms.

Compounds are made through a chemical change. The elements form chemical bonds between the atoms. A chemical bond is the force of attraction the holds atoms in a molecule together. A chemical change can also change a compound back into an element. To do this, the chemical bonds have to be broken. Heating is one of the ways that this is done. Examples: As you know the chemical formula for sugar is C 6 H 12 O 6. Well when you heat sugar it melts. If you heat the melted sugar long enough the oxygen and hydrogen will break away from the carbon and become gases. The carbon will remain in the test tube.

Another way to break apart bonds are through electricity.

What is a mixture? Two or more substances that have been PHYSICALLY combined. What are some examples of a mixture? Salad, sugar and cinnamon, salt water, sugar and water.

There are two kinds of mixtures. Even mixtures and uneven mixtures. Think about a salt water mixture. There are even amounts of salt and water. Salt is still salt and water is still water but they are so evenly distributed that they look all the same. They do have all of their own properties.

Now think of a salad. This is an example of an uneven mixture. In this mixture, each item in the mixture has all of its own properties. So a tomato is still a tomato and lettuce is still lettuce.

Knowing the difference properties of the items in a mixture can help you to separate them. This is because parts of a mixture are not chemically combined. This means that you can separate them by their physical properties. In the salad, the tomatoes can be picked out manually.

How do you think that you would separate the salt water mixture? You would have to boil the water. When you boil water, the water evaporates and all the you would be left with is the salt.

Other mixtures can be separated by filtering. Example: Sand and water can be separated through filtering. You would use a funnel with filter paper to pour the mixture through. The water would go through the filter paper and the sand would not.

So how exactly are mixtures different than compounds? Compounds are combines chemically where mixtures are combine physically. You can separate a mixture manually by their physical means but a compound you have to separate chemically with heat or with electricity.

What are iron fillings? Small sliver or shavings of the element iron.

What is sulfur? An element on the periodic table that is not a metal. It is a yellowish substance.

How would you separate this mixture? You would separate it by using a magnet. The iron is a metal and all metals are attracted to a magnet. The sulfur is not a metal so it is not attracted to a magnet.

How are compounds made? Form as a result of a chemical change. Made of two or more elements that are chemically combined. Examples: Molecules of salt are combined by a chemical change. Sodium atoms form bonds with chlorine atoms to produce salt molecules.

Can iron and sulfur combine chemically also? Yes they can…it is called iron sulfide. It forms when iron fillings and sulfur are mixed then heated.

There are many differences between mixtures and compounds. A mixture has no definite chemical composition. Each item contains its own properties in a mixture. A mixture can be separated by physical means.

A compound has a definite chemical composition. Elements lose their physical properties when they become chemically combined. They cannot be separated by physical means.

Ionic Bonding Chemical bonds are formed through the use of valence electrons. Valence electrons: electrons in the outmost energy level of an atom.

The outermost energy level contains up to 8 valence electrons; except for hydrogen and helium: their outermost energy level only contain up to 2 valence electrons.

All the atoms of all the elements have valence electrons. Atoms with fewer that 8 valence electrons form bonds with other atoms. Atoms can either gain electrons, lose electrons or share electrons. When they do this…it makes them more stable.

What is all matter made of? ATOMS!!!!

What are the smaller particles that make up an atom and what are their charges? Proton: positive charge in the nucleus Neutron: no charge in the nucleus Electron: negative charge surrounding the nucleus

What makes an atom neutral? The number of protons and electrons are the same in every atom.

When chemical bonds are formed, nonmetals are going to gain electrons. Metals are going to lose electrons. When this happens the number of protons is going to be different than the number of electrons and the atoms becomes electrically charged.

What is an ion? Atom with an electrical charge.

A neutral atom that gains electrons becomes a negative ion. A neutral atom that loses electrons becomes a positive ion.

Why does this happen? This happens because if an atom loses electrons, then the nucleus has a greater number of protons than electrons meaning the nucleus has a greater positive charge. When an atom gains electrons, there will be greater negative charge outside of the nucleus then a positive charge inside the nucleus because there are now more electrons in the atom than protons.

Compounds are held together by chemical bonds. What is an ionic bond? A bond formed between atoms that have gained or lost electrons.

What are ionic compounds? Compounds held together by ionic bonds. Not made of molecules Made up instead by one or more positive ions and one or more negative ions. All ionic compounds have similar properties One property is that they become crystals. Have high melting points Conduct electricity when they are melted.

Covalent Bonding As you have noticed with the periodic table, not all the elements have their outermost energy levels full. Because of this, atoms are either going to gain, lose or share electrons. The electrons are going to come from other atoms that also have incomplete outermost energy levels.

How are ionic compounds formed? When atoms gain one or more electrons and other atom loses one or more electrons. Opposites attract making an ionic compound.

Elements also form compounds when they share electrons. When atoms bond this way, the bond is called a covalent bond.

Covalent compounds: compounds whose atoms share electrons in covalent bonds. Water is an example of a covalent bond.

Here is what it looks like:

So what are the differences between ionic and covalent bonds? Atoms in Ionic Bonds gain or lose electrons. Atoms in covalent bond share electrons. This means that the atoms do not become positively or negatively charged. The atoms remain neutral. You can use electron dot diagrams to show how covalent bonds form and how electrons are shared.