KEY TAKEAWAYS Key Points An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons, and the outer region of the atom, which holds its electrons in orbit around the nucleus. Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams,…
Dalton’s Atomic Theory
Although a schoolteacher, a meteorologist, and an expert on color blindness, John Dalton is best known for his pioneering theory of atomism. He also developed methods to calculate atomic weights and structures and formulated the law of partial pressures. Early Life Dalton (1766–1844) was born into a modest Quaker family in Cumberland, England, and for…
Atoms, Molecules, and Ions
Anion & Cation An anion is a negatively charged ion. Non-Metals typically form anions. A cation is a positively charged ion. Metals typically form cations. Atom An atom is the smallest particle of an element that retains the chemical properties of that element. So we’re talking some super-tiny stuff here. Atoms are electrically neutral, with…
Density Measurements
A material’s density is defined as its mass per unit volume. Put another way, density is the ratio between mass and volume or mass per unit volume, explains Study.com, adding: “It is a measure of how much stuff an object has in a unit volume (cubic meter or cubic centimeter).” Density is, essentially, a measurement of…
Significant Figures in Calculations
Significant figures refer to the number of important single digits in the coefficient of an expression in scientific notation on which they carry meaning that contributes to the accuracy of a measurement. The number of significant figures in an expression indicates the confidence or precision of a quantity. It is important for cases or investigations…
Accuracy and Precision
Accuracy Accuracy refers to the closeness of a measured value to a standard or known value. For example, if in lab you obtain a weight measurement of 3.2 kg for a given substance, but the actual or known weight is 10 kg, then your measurement is not accurate. In this case, your measurement is not…
Methods of Separating Mixtures
Mixtures come in many forms and phases. Most of them can be separated, and the kind of separation method depends on the kind of mixture it is. Below are some common separation methods: Paper Chromatography This method is often used in the food industry. It is used to identify chemicals (coloring agents) in foods…
Classification of Matter
PURE SUBSTANCES A pure substance has a definite and constant composition — like salt or sugar. A pure substance can be either an element or a compound, but the composition of a pure substance doesn’t vary. MIXTURES Mixtures are physical combinations of pure substances that have no definite or constant composition — the composition of a mixture varies…
States of Matter
There are five known phases, or states, of matter: solids, liquids, gases, plasma and Bose-Einstein condensates. The main difference in the structures of each state is in the densities of the particles. Solids In a solid, particles are packed tightly together so they are unable to move about very much. Particles of a solid have…
The Particulate Nature of Matter
The entire universe is made of two things: matter and energy. For the time being we will concern ourselves with matter only. I. Matter Matter is defined as that which has mass and occupies space. This definition seems simple enough, yet there are profound issues which surround it. For example, there is currently no generally…
Senior Chemist 