Unit 1 sets up the whole course by explaining what chemistry studies, how to work safely in a chemistry lab, and how to describe and classify matter. By the end, you should be able to sort any sample into an element, compound, or mixture, tell physical changes from chemical ones, and explain the reason behind each lab safety rule.
Read the big ideas first, then work through each topic note and try its check-yourself question before moving on.
This is the foundation unit. It has less math than later units, but the vocabulary here shows up everywhere else in the course. If you can use words like compound, homogeneous mixture, and chemical change correctly, later topics like reactions and stoichiometry get much easier.
Honors Chemistry Unit 1 covers three things. First, it covers what chemistry is and why it's called the central science, plus the history that made it a measurement-based science (Lavoisier's careful measurements supporting conservation of mass, Dalton's atomic theory, Mendeleev's periodic table). Second, it covers lab safety, including PPE, lab conduct, waste disposal, Safety Data Sheets, and emergency equipment. Third, it covers matter itself: the three common states of matter under ordinary lab conditions and the six phase changes among them, physical versus chemical properties and changes, and how to classify a sample as an element, compound, or mixture.
Matter is anything with mass that takes up space, so chemistry connects to biology, physics, earth science, medicine, and engineering. That overlap is why chemistry gets called the central science. Lavoisier's careful measurements in the late 1700s helped turn it into a science built on measurement.
Chemical splash goggles reduce the chance of eye exposure, while properly selected gloves reduce skin exposure. Nitrile works with many chemicals but not all, so check the SDS and your teacher's instructions. A Safety Data Sheet tells you the hazards and first aid for a hazardous chemical product. If you know why a rule exists, you'll follow it even when nobody is watching.
Under ordinary lab conditions, the samples in this unit are solids, liquids, or gases, depending on how their particles are arranged and how they move. Matter can also exist in other states, such as plasma. A sample's makeup is either a pure substance (an element or compound) or a mixture. Physical changes leave chemical identity unchanged, while chemical changes form new substances.
Ice holds its shape because its particles vibrate around fixed positions, and a sand-water mixture can be filtered because the insoluble sand particles are larger than the filter pores. Both of those visible facts come from what particles are doing. Lab safety rests on the same idea, since the danger of a chemical comes from how its particles react with your skin, eyes, or other chemicals. Get used to asking what the particles are doing, and the rest of the course will make more sense.
Chemistry is the study of matter, its properties, and the changes it undergoes.
Lab accidents can result from unsafe procedures, equipment problems, chemical hazards, or human error, so follow the approved procedure every time.
Under ordinary lab conditions, matter shows up in three common states.
Chemistry is the study of matter, its properties, and the changes it undergoes. It's called the central science because other sciences depend on it. Biologists need it to explain how enzymes work, geologists use it to explain how minerals form, and doctors rely on it for drugs and blood tests.
Modern chemistry grew out of a few big steps. In the late 1700s, Antoine Lavoisier's careful measurements helped establish that mass stays constant in a chemical reaction, which moved chemistry away from alchemy and toward measurement. In the early 1800s, John Dalton proposed that each element is made of its own kind of atom and that atoms combine in fixed ratios. In 1869, Dmitri Mendeleev arranged the elements into a periodic table and used the gaps to predict elements like gallium and germanium before anyone found them. In the early 1900s, quantum theory explained why electrons behave the way they do.
Chemistry has costs as well as benefits. Work in chemistry and biochemistry helped turn penicillin into a usable medicine and produced materials such as nylon. Chemical research also produced CFCs, which damaged the stratospheric ozone layer.
Worked example. You burn 2.43 g of magnesium in oxygen and collect 4.03 g of magnesium oxide. How much oxygen reacted? Mass is conserved, so the mass of the reactants equals the mass of the product. , so of oxygen.
Check yourself: A log loses mass as it burns. Does this break the law of conservation of mass? (Answer: No. The missing mass leaves as carbon dioxide and water vapor. If you captured those gases, the total mass of the products would equal the mass of the wood plus the oxygen that reacted.)
Lab accidents can result from unsafe procedures, equipment problems, chemical hazards, or human error, so follow the approved procedure every time. Your protection starts with PPE (personal protective equipment). Wear chemical splash goggles, because regular glasses and open-sided safety glasses let liquids in from the sides. Nitrile gloves resist many common lab chemicals and avoid latex allergy concerns, but they do not protect against every substance. Use the glove type specified by the SDS or your teacher, and remove contaminated gloves promptly. Wear the lab coat or apron specified for the experiment, closed-toe shoes, and tied-back hair. Cotton does not melt like many synthetic fabrics, but ordinary cotton clothing is not flame-resistant.
Don't eat or drink in the lab or run experiments your teacher hasn't approved. When you dilute an acid, add the acid to the water so the heat spreads through a large volume.
Put waste only in the labeled container assigned by your teacher, never the sink unless your teacher says so. Don't combine waste based only on broad labels such as acid, base, or organic, because chemicals within those groups can still react dangerously. Report every spill and every piece of broken glass right away.
Manufacturers and suppliers provide an SDS for each hazardous chemical product. An SDS has 16 standard sections. Section 2 covers hazards and GHS pictograms, Section 4 covers first aid, and Section 9 lists physical properties such as boiling point. In an emergency, use the eyewash station for eye exposure and the safety shower for substantial skin or clothing exposure. Begin flushing immediately for at least 15 minutes, follow the SDS if it calls for longer rinsing, and tell your teacher at once.
Check yourself: Your lab partner splashes a dilute acid into one eye. What should happen first, and for how long? (Answer: Get them to the eyewash station right away and flush the eye for at least 15 minutes while someone tells the teacher. Check Section 4 of the SDS for any further first aid or a longer rinse time.)
| Hazard | What protects you | Why |
|---|---|---|
| Splash to the eyes | Chemical splash goggles | Glasses leave gaps at the sides and bottom |
| Chemical on skin | Gloves and a lab coat or apron chosen for the chemical | Properly selected PPE reduces skin exposure. Check chemical compatibility and remove contaminated PPE promptly. |
| Open flame | Tied-back hair, cleared flammables, and any heat-resistant PPE required for the procedure | Hair and flammable materials can ignite, and ordinary cotton clothing is not flame-resistant |
| Mixing incompatible waste | The labeled waste container your teacher assigns | Some waste combinations release heat or toxic gas |
Under ordinary lab conditions, matter shows up in three common states. Solid particles are packed tightly and vibrate in place, so solids keep a fixed shape and volume. Liquid particles stay close but slide past each other, so liquids keep their volume but take their container's shape. Gas particles are far apart and move fast and randomly, so gases fill their container and compress easily.
Six phase changes connect these states. Melting, vaporization, and sublimation (solid straight to gas, like dry ice) absorb energy. Freezing, condensation, and deposition (gas straight to solid, like frost) release energy.
A pure substance is either an element (one kind of atom, like copper) or a compound (elements chemically bonded in a fixed ratio, like H₂O). A mixture is a physical blend. Homogeneous mixtures like salt water look the same throughout, while heterogeneous mixtures like sand and water don't. Filtration, evaporation, distillation, and chromatography separate mixtures by physical means.
Physical changes, such as melting or dissolving sugar in water, leave the substance's chemical identity unchanged. Chemical changes, such as rusting or burning, form new substances.
Worked example. A metal block has a mass of 54.0 g and a volume of 20.0 cm³. Density is . That equals the commonly cited density of aluminum, so aluminum is a possible identity, but density alone does not prove the block's composition. It's greater than water's 1.00 g/cm³, so the block sinks.
Check yourself: Sugar dissolves completely in tea. Is the sweet tea a compound or a mixture, and is dissolving a physical or chemical change? (Answer: It is a homogeneous mixture, and dissolving sugar is a physical change. The sugar molecules remain sugar. Evaporating the water would leave the dissolved solids behind, but it would not separate the sugar from the other substances in tea.)
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes container's shape | Takes container's shape |
| Volume | Fixed | Fixed | Fills the container |
| Particle spacing | Tightly packed | Close but able to slide | Far apart |
| Particle motion | Vibrate in place | Slide past each other | Fast and random |
| Compressibility | Very low | Very low | High |
| Term | Definition |
|---|---|
| Matter | Anything that has mass and takes up space, including solids, liquids, and gases. |
| Central science | A name for chemistry because it connects physics, biology, earth science, and medicine. |
| Law of conservation of mass | The principle that the total mass remains constant during an ordinary chemical reaction in a closed system, which Lavoisier's careful measurements helped establish in modern chemistry. |
| Safety Data Sheet (SDS) | A standardized 16-section document for a hazardous chemical product that lists its hazards, first-aid steps, and safe handling. |
| Element | A pure substance made of only one kind of atom that can't be broken down by chemical means, such as oxygen or iron. |
| Compound | A pure substance of two or more elements chemically bonded in a fixed ratio, such as water or sodium chloride. |
| Heterogeneous mixture | A mixture whose parts are unevenly spread and often visible, such as sand in water or a salad. |
| Chemical change | A change that produces a new substance with different properties, such as iron rusting or wood burning. |
| Sublimation | A phase change in which a solid turns directly into a gas without becoming a liquid, as dry ice does at room temperature. |
| Density | Mass divided by volume, usually written in g/cm³ or g/mL, which tells you how much mass is present in a given volume. |
Salt seems to disappear in water, so it looks like something new formed. It hasn't. The salt is still there, and evaporating the water brings it back. Ask whether a new substance with new properties formed. Gas from a reaction, a new color, or a permanent new solid point to a chemical change. Melting and freezing are physical changes. Dissolving is also physical when the dissolved substance keeps its chemical identity, as salt does in water.
Salt water looks perfectly uniform, so it's tempting to call it pure. Uniform appearance only tells you a mixture is homogeneous. A pure substance has a fixed composition, while salt water can be 1% salt or 10% salt and still be salt water. If you can change the ratio of the parts, it's a mixture.
Prescription glasses are not chemical splash protection because liquids can enter from the sides or below. Wear approved chemical splash goggles over your glasses. Splash goggles do not necessarily protect against vapors, so use ventilation and any other protection required by the SDS and your teacher.
A burning candle or a fizzing antacid tablet seems to get lighter, which looks like mass disappeared. The mass left as gas you couldn't see. In a closed container, the total mass stays the same, which is what the law of conservation of mass says.