Alani G7 Atoms & Elements Unit REVIEW Notes PDF

What is matter? Anything made of atoms or atomic particles Anything that takes up space (volume) and/or has mass.  What is an atom? The smallest complete unit of matter  Atomic number The element’s symbol The element’s name Atomic mass (atomic weight) The number of protons...

What is matter? Anything made of atoms or atomic particles Anything that takes up space (volume) and/or has mass.  What is an atom? The smallest complete unit of matter  Atomic number The element’s symbol The element’s name Atomic mass (atomic weight) The number of protons The number of protons and neutrons  Atomic mass is protons + neutrons Be mindful. There is a good chance you will forget this. It is notoriously difficult to remember this for some reason.  Sometimes, when we are calculating the number of neutrons, we may round the atomic mass number to the nearest whole number to avoid using decimals. To do this, look at the first decimal place. Ignore the second decimal place. Chlorine 35.45 = 35 Copper 63.54 = 64 Protons are located in the nucleus. Protons have a positive charge (+). Neutrons are also found in the nucleus. Neutrons have neutral charge or no charge (0) Electrons are found in the electron cloud. Electrons have negative charge (-)  The charges of atomic particles-(protons & electrons) can be thought of like the poles of a magnet. Like charges repel, opposite charges attract. What makes one element different from another? For example; why is “helium” helium and not lithium? It is all about how many protons it has. All helium in the universe has 2 protons. If it has more than 2 protons or less than 2 protons, it is not helium.  What is an element? Not all atoms are the same. Each type of atom has its own name. Each type of atom is a different element. Knowing the name of the element tells you what type of atom it is.  Isotope - means different versions of an element. While that element will always have the same number of protons, some atoms of that element may not all have the same number of neutrons. This is what I mean by different versions. Isotope Carbon-12 has 6 neutrons. Isotope Carbon-13 has 7 neutrons. Carbon isotopes  Hydrogen isotopes Hydrogen-1 Hydrogen-2 Hydrogen-3  Lithium isotopes Lithium-6 Lithium-7 Lithium-8 The reason atomic mass always has decimals  Ion - means an atom with a charge. (An atom that is NOT neutral) If the atom has a different number of protons compared to electrons then it will have either a positive charge or a negative charge. If an atom has the same number of protons and electrons then it does not have charge and is not an ion.  Protons Neutral Atom atom Electrons Atom Atom  Mixtures Salt + Water Salt + Water Saltwater No Chemical Reaction bonded together bonded together Difference between molecules and compounds Hint: All compounds are molecules but not all molecules are compounds.  Difference between molecules and compounds If an atom is bonded to any other atom then it is a molecule. So if it is an atom just by itself, then it’s just an atom, not a molecule.  Difference between molecules and compounds If an atom of one element is bonded to a different element then you can call it a molecule or a compound. The air we breathe is mostly a mixture of molecules (NOT COMPOUNDS) and argon atoms. Most of the gas in the air is nitrogen (N2), which makes up about 78% of air. Oxygen (O2) is the second most abundant gas at about 21%. The gas argon (Ar) is the third most abundant gas at 0.93%. Chemical Equations Chemical Reaction What is a chemical reaction? A process that involves the rearrangement of the atoms in molecules to make different molecules. A chemical change that occurs when two or more substances combine to form a new substance What are the indicators that a chemical reaction has occurred? How might you know if a chemical reaction has happened?  Indicators of a chemical reaction Change in Color: One of the most apparent indicators is a change in color. When the color of the reactants is different from that of the products, it often signifies a chemical reaction. For example, the browning of apples when exposed to air is due to a chemical reaction. Formation of Precipitate: When two clear solutions are mixed, and a solid substance forms and settles at the bottom, it's called a precipitate. This usually indicates a chemical reaction between the two solutions. Evolution of Gas: The release of a gas can be a sign of a chemical reaction. For instance, when baking soda and vinegar are combined, they produce carbon dioxide gas, leading to bubbles and fizzing. Change in Temperature: Some chemical reactions absorb heat from their surroundings, causing a decrease in temperature (endothermic reactions), while others release heat, causing an increase in temperature (exothermic reactions). Sensing a temperature change can indicate a reaction.  Indicators of a chemical reaction Release or Absorption of Light: Some reactions produce light as a product (chemiluminescence), while others may absorb light. These changes in light emission or absorption can indicate a chemical reaction. Odor Change: A change in odor can be a strong indicator of a chemical reaction. New and distinct odors can be produced when certain substances react with one another. Change in Texture or State: If there is a significant change in the texture or state of the substances involved, it can indicate a chemical reaction. For example, when a solid dissolves in a liquid, or when a liquid evaporates to form a gas, these are often signs of chemical changes. Change in Mass: A change in mass can also be an indicator. In a closed system, the total mass before and after a reaction should remain constant according to the law of conservation of mass. However, if gases are involved and not contained, there can be a change in apparent mass due to the loss or gain of gases. Change in pH: If the pH of a solution changes significantly, it may indicate a chemical reaction. For example, the neutralization of an acid with a base results in a change in pH towards neutrality. Link to explanation for balancing equations Link to good practice for the Summative A: Go to the “Game” section