Atoms and Elements: A Simple History & Overview PDF

### A Simple History of the Atom **Dalton’s Model (1803):** - Dalton thought atoms were like tiny, solid balls that couldn't be divided. - Atoms combined in whole-number amounts to make things. - Picture: Imagine a solid ball, like a pool ball. **Thomson’s Model (1897):** - Thomson discovered that...

### A Simple History of the Atom **Dalton’s Model (1803):** - Dalton thought atoms were like tiny, solid balls that couldn't be divided. - Atoms combined in whole-number amounts to make things. - Picture: Imagine a solid ball, like a pool ball. **Thomson’s Model (1897):** - Thomson discovered that atoms have tiny, negatively charged particles called electrons. - He thought atoms were positively charged with electrons stuck inside, like a chocolate chip cookie. - Picture: A ball with little dots (electrons) inside it. **Rutherford’s Model (1909):** - Rutherford found that most of an atom is empty space. The center has a small, dense core (nucleus) with a positive charge, and electrons move around it. - Picture: A tiny center (nucleus) with electrons spinning around it. **Bohr’s Model (1913):** - Bohr said that electrons orbit the nucleus in certain paths or energy levels, like planets around the sun. - Picture: A center (nucleus) with electrons in rings around it. ### Understanding the Atom **1. Lithium Atom:** - Proton: Positively charged particle in the nucleus. - Neutron: Neutral particle in the nucleus. - Electron: Negatively charged particle around the nucleus. **2. Atomic Number and Mass:** - The atomic number equals the number of protons in an atom. - The number of electrons equals the number of protons. - The total particles in the nucleus equal the atomic mass rounded off. - The number of neutrons equals the total particles minus the protons. **3. Ion Charge of a Lithium Ion:** - A lithium ion loses an electron. - Charge: 3 positive protons - 1 negative electron = 2+ charge. **4. Reactions and Charges:** - Alkali metals give 1 electron, so their ion charge is 1+. - Alkaline earth metals give 2 electrons, so their ion charge is 2+. - Halogens gain 1 electron, so their ion charge is 1-. - Noble gases don’t react, and their charge is 0. ### Safety Symbols - **WHMIS**: Workplace Hazardous Materials Information System. - **MSDS**: Material Safety Data Sheet. WHMIS symbols warn about dangers like: - **Gas Cylinder**: For gases under pressure. - **Flame**: Fire risks. - **Exploding Bomb**: Explosion risks. - **Health Hazard**: Serious health problems. - **Skull and Crossbones**: Deadly toxins. - **Corrosion**: Can damage skin or metals. - **Environmental Hazard**: Harms the environment. - **Biohazard**: Causes diseases. ### Physical Properties of Matter **Matter** is anything with mass that takes up space. Physical properties describe what matter looks like or how it behaves without changing its chemical structure. Examples: - Appearance: Color, texture, luster (shine). - State: Solid, liquid, gas. - Boiling and freezing points. - Density: How much stuff is packed into a space. - Malleability: How easily something can be flattened. - Ductility: How easily something can be stretched into a wire. Physical properties can be: - **Intensive**: Don’t depend on the amount (e.g., color, boiling point). - **Extensive**: Depend on the amount (e.g., volume, mass). **Chemical properties** are things we can only know about a substance when we change it into something else. For example, we find out if something can catch on fire by burning it. **Physical properties** are things we can observe or measure without changing what the substance is. For example, you can measure the mass or volume of water without changing it into something else. ### Types of Properties | Property Type | Do we have to change the substance to find out? | Does the amount of substance matter? | Examples | |-----------------------|------------------------------------------------|--------------------------------------|----------- -----------------------| | **Physical** | No | No | Lustre (shininess), state (solid, liquid) | | **Chemical** | Yes | No | Flammability, reactivity | | **Intensive Physical** | No | No | Color, odor, density | | **Extensive Physical** | No | Yes | Mass, volume, length | **Task 4: More Examples** | Property Type | Examples | |-----------------------|-----------------------------------------------| | **Intensive Physical** | Color, odor, melting point, boiling point | | **Extensive Physical** | Length, width, height, weight | ### Other Ways to Classify Matter You can also group matter by: - **State:** Is it a solid, liquid, or gas? - **Composition:** Is it made of one element, a compound, or a mixture of different things? - **Particle arrangement:** Is it ordered like crystals, or random like a soft material? - **Conductivity:** Can it conduct electricity? - **Magnetism:** Is it magnetic? These different ways help us better understand how matter behaves. ### Physical and Chemical Changes to Matter (Simplified) There are two main types of changes that matter can go through: **physical changes** and **chemical changes**. ### Physical Change A **physical change** happens when something changes its shape, size, or form, but it stays the same substance. * **Examples:** * Water turning into ice * Dissolving salt in water * Breaking a rock  * Tearing a piece of paper ### Chemical Change A **chemical change** happens when something reacts and turns into a completely new substance. * **Examples:** * Baking bread * Fireworks exploding * Burning wood * Cooking an egg ### How to Tell the Difference | **Physical Change Signs** | **Chemical Change Signs** | |---|---| | Change in state (solid, liquid, gas) | New color appears | | Change in shape or size | New smell (odor) | | Temperature goes up or down | New texture | | Change in volume (space it takes up) | Gas or bubbles form | | | A solid forms from a liquid | **Note:** Physical changes can often be undone (like melting ice back into water), but chemical changes usually can't be reversed (like burning wood to ash). We are most concerned with electrons, which are part of the atom involved in chemical reactions. Electrons are found outside the nucleus in a space called the electron cloud. They are organized in energy levels or orbitals/shells. Bohr models are used to predict reactivity in elements. Reactivity is how likely an element is to form a compound with another element. When looking at Bohr models, we look at its valence electrons. Valence electrons - electrons on its last energy level Drawing Bohr Models 1. Draw the Nucleus. 2. Write the number of neutrons and protons in the nucleus. 3. Draw the first energy level. 4. Draw the electrons in energy levels according to the rules. Keep track of electrons in each level. Rules for Energy Levels 1. Level 1 (closest to the nucleus) can hold a maximum of 2 electrons. 2. Level 2 can hold a maximum of 8 electrons. 3. Level 3 can hold a maximum of 8 electrons. 4. Level 4 can hold a maximum of 32 electrons. You must fill one energy level before going on to draw the next level. Ionic Compounds: A Simple Explanation Imagine a dance party. Metal atoms are like shy boys who don't like to hold onto things. They want to give away their extra stuff. Nonmetal atoms are like greedy girls who love to collect things. They want to take the extra stuff from the boys. When a metal atom (shy boy) meets a nonmetal atom (greedy girl), they do a trade. The metal atom gives away its extra stuff (electrons), and the nonmetal atom takes it. This is called electron transfer. After the trade: The metal atom is happy because it got rid of its extra stuff. It's now a positive ion (cation). The nonmetal atom is happy because it got more stuff. It's now a negative ion (anion). These happy, trading atoms stick together really tightly. They form a solid at room temperature. They're also brittle like a cookie - they can break easily. When you heat these compounds or dissolve them in water, the atoms can move around freely. This makes them conductors - they can carry electricity. Remember: Ionic compounds are always made of a metal and a nonmetal. Improved Text: Prefixes for Number of Atoms Prefix Number of Atoms Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10 Example: Diphosphorus pentoxide Two phosphorus atoms Five oxygen atoms Chemical formula: P₂O₅ Note: When there is only one atom of the first element, "mono-" is usually not used. For example, CO is carbon monoxide. Writing Formulas for Molecular Compounds When writing formulas for molecular compounds, you will not be expected to determine the state of the compound at room temperature.