| A | B |
|---|
| What is the basic unit of matter? | The atom is. |
| Who coined the word "atom"? When? | Democritus named the term nearly 2500 years ago. |
| What subatomic particles make up an atom? | It's made up of protons, neutrons, and electrons. |
| What similarities do protons and neutrons have? | Both have about the same mass, and strong bonds bind them together to form the nucleus. |
| What differences are there between protons and neutrons? | Protons or positively charged ("pro"); neutrons have no charge. |
| Why are atoms neutral in their charge? | They have equal numbers of electrons and protons, and those subatomic particles have equal but opposite charges. |
| What charge does an electron have and how much does mass does it have? | Its mass is 1/1840 the mass of a proton; they are negatively charged. |
| What is a chemical element? How many are there? | It's a pure substance that's made up of one type of atom. There are over 100 known elements. |
| How do you know the atomic numer of an element? | It's the number of protons in the atom. |
| What is an isotope? | It's an atom of an element that has a number of neutrons different from that of other atoms of the same element. (In other words, atoms of the same element that differ in the number of neutrons they contain.) |
| How can you find the mass number of an atom? | It's the sum of the protons + neutrons in the nucleus of an atom. |
| How is an isotope identified? | They're identified by their mass numbers. |
| How is the atomic mass calculated? | It's an average: total mass of an elements isotopes divided by the number of isotopes in the element. |
| Why do isotopes of an element have the same chemical properties? | It's because they have the same number of electrons. |
| What does it mean when an isotope is radioactive? | It has a nucleus that's unstable and breaks down at a constant rate over time. |
| What are some practical uses of radioactive isotopes? | 1) Geologists determine rock and fossil ages by studying the isotopes in them; cancer is treated with some; bacteria can be killed by them; they can be used as tracers to follow movement of substances in an organism. |
| What's a chemical compound? | It's a substance formed by the chemical combination of 2 or more elements in definite proportions (see pg. 37). |
| What's a chemical formula? | It's the shorthand used to show the composition of compounds; it shows the types of elements that are in the compound and the ratio in which atroms of those elements combine. |
| What's the formula for table salt? | It's NaCl. (sodium + chlorine in a 1:1 ratio--1 sodium + 1 chlorine) |
| What are the 2 main types of chemical bonds? | They're ionic and covalent bonds. |
| How is an ionic bond formed? | It's formed when 1 or more electrons are transferred from 1 atom to another. |
| What charge do ions have? | Some are positive; some are negative. If an atom loses electrons, it has a + charge; it the atom gains electrons, it has a - charge. |
| Actually, what is an ionic bond? | It's the strong attraction between oppositely charged ions. |
| When is a covalent bond formed? | It's formed when electrons are shared between atoms. |
| How is a double covalent bond formed? | It's formed when 4 electrons are shared by atoms. |
| What's a triple bond? | It's when 6 electrons are shared by atoms (see page 38). |
| What is a molecule? | It is the structure resulting when atoms are joined together by covalent bonds; it's the smallest unit of most compounds. |
| What are van der Waals forces? | They're the slight attranctions that develop between oppositely charged regions of nearby molecules. They're not as strong as ionic or covalent bonds. |
| How does a gecko climb up a wall? | Van der Waals forces form between molecules on the surface of the gecko's foot and molecules on the surface of the wall; the combined strength allows the gecko to balance the pull of gravity. |
