Grade 7 Science: Atoms, Elements, Compounds, and Mixtures Notes

Grade 7 Science Atoms, Elements, Compounds and Mixtures Elements An element is a pure substance that cannot be broken down. A list of these elements is called the “Periodic Table”. Elements can form compounds. Different elements combine together to form compounds. Each element has a symbol (peri...

Grade 7 Science Atoms, Elements, Compounds and Mixtures Elements An element is a pure substance that cannot be broken down. A list of these elements is called the “Periodic Table”. Elements can form compounds. Different elements combine together to form compounds. Each element has a symbol (periodic table). Examples:  C – Carbon  H – Hydrogen  O – Oxygen  Na – Sodium Many elements have names that have come from Latin. What are Atoms? Atoms are the smallest unit of a substance. Atoms are microscopic. Atoms have three basic parts: protons, neutrons and electrons. The protons and neutrons are in the middle and the electrons move around them. The centre of the atom is called the nucleus and the electrons orbit the nucleus in electron shells. Grade 7 Science Grade 7 Science Compounds Small groups of atoms are called molecules. Larger structures are called lattices. Special forces called atomic bonds hold the atoms together. Water is H2O Oxygen is O2 H H O O O Carbon Dioxide is CO2 O O C Grade 7 Science A compound is made up of lots of the same molecules joined together separately or in a lattice. Compounds can have very different properties than the elements they contain. E.g. Water is a liquid at room temperature but the elements Hydrogen and Oxygen are colourless gases. Compound formulas When atoms bond together we describe this by writing a formula about how they have combined. This formula is known as a chemical formula. Example 1 - Water, the scientific name is dihydrogen oxide, the formula is H2O, the structure is a molecule, it is made up of 2 hydrogens and 1 oxygen. Example 2 – Table salt, the scientific name is sodium chloride, the formula is NaCl, the structure is a lattice, it is made up of 1 sodium and 1 chlorine. Mixtures A mixture contains two or more substances (elements or compounds). These substances are not bonded and no new substance is formed. A mixture can therefore be separated, for example by filtration or evaporation. Grade 7 Science WHOLE LOTTA RULES GOING ON The process is just a set of rules. We're going to show you some of the basics. There are some advanced ways of naming things that we're going to skip right now. Let's start with some basic rules. When you have two different elements, there are usually only two words in the compound name. The first word is the name of the first element. The second word tells you the second element and how many atoms there are in the compound. The second word also ends in IDE. That's the suffix. When you are working with non-metals like oxygen (O) and chlorine (Cl), the prefix (section at the beginning of the word) of the second element changes based on how many atoms there are in the compound. It's like this. Do you notice anything about the chalkboard? You can see that the prefixes are very similar to the prefixes of geometric shapes. You know what a triangle is. Right? Well the prefix tri- means three. So when you have three chlorine (Cl) atoms, you would name it trichloride. Grade 7 Science Look at the other names, too. You may know about a pentagon, a hexagon, or an octagon. The naming system in chemistry works the same way! Let's put these ideas together! Remember, we're only talking about simple compounds with no metal elements. Most simple compounds only have two words in their names. Let's start with Carbon monoxide (CO). You have one carbon (C) atom and one oxygen (O) atom (you can also use the prefix MONO to say one atom). Remember that the second word ends in -ide. So... (1) Carbon + (1) Oxygen = Carbon monoxide Now we'll build on that example. What if you have one carbon (C) and two oxygen (O) atoms? (1) Carbon + (2) Oxygen = Carbon dioxide One last example and we'll call it quits. Now you have one carbon (C) and four chlorine (Cl) atoms. (1) Carbon + (4) Chlorine = Carbon tetrachloride You should be getting the idea now. The compound name can tell you how many atoms are inside. Take a look at some of the examples and see if you understand what is happening in the name. Grade 7 Science Grade 7 Science Answers: 1. Name 3 elements starting with C. Carbon, Chlorine, Cobalt 2. Name 6 elements with single letter symbols. Hydrogen (H), Boron (B), Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), Sulfur (S) 3. What are the names of these elements? a. Na Sodium b. Li Lithium c. N Nitrogen d. K Potassium e. Cu Copper f. Ti Titanium 4. Write the chemical formula for each of these: a. Water H2O b. Carbon dioxide CO2 c. Oxygen O2 d. Table salt NaCl e. Hydrochloric acid HCl 5. How many of each type of atom is in a molecule of: a. H2O 2 hydrogen, 1 oxygen b. CH4 1 carbon, 4 hydrogen c. C8H18 8 carbon, 18 hydrogen d. Fe2O3 2 iron, 3 oxygen 6. Give one example of how you could separate a mixture. Grade 7 Science Evaporation or Filtration