Writing in Science
Because of society relies heavily on written expression and printed material, it is important for you to posses effective writing skills. You will be expected to:
Everything is made up of chemicals; you, your clothes, the soda you drank at lunch (which is now under your desk), the medicines we take, the shampoo you use, the food we eat, and the list goes on and on.
Chemistry is the study of all substances and the changes that they undergo. Chemists strive to satisfy their own curiosity by answering the questions of WHY things happen the way they do.
Measuring in Science
Everything in our world is made of atoms, which we can visualize as
negatively charged electrons orbiting rapidly around a nucleus,
composed of positively charged protons and neutral neutrons.
The different types of atoms are called the chemical elements, substances
that do not break down into simpler substances by chemical means. There
are 90 elements found naturally on Earth, but there are 109 presently on the periodic
table of the elements.
Protons and neutrons have more mass than electrons, so we find an atom’s total mass using only the masses of its nuclear particles. Hydrogen has a mass of 1.67 x 10 -24 grams, about one atomic mass unit (u). To find an atom's mass, simply find its mass number on the periodic table. All elements have isotopes, forms of elements with different numbers of neutrons in the nucleus. The number of protons in a nucleus, its atomic number, shows identity. If the number of protons change, then it becomes a different element. The atomic number also determines the number of electrons in a neutral atom which also determines its chemistry.
Periodic Table Notation
Elements increase in atomic number across each period, and down each group.
Isotopes are atoms of the same element with different numbers of neutrons (mass). They react chemically the same as the normal form of the element and are normally radioactive.
Example Isotopes: Hydrogen
hold atoms together. The electric force, a force vastly
stronger than gravity, holds an atom's electrons in the space around its
nucleus. The nuclear force holds an atom's protons and neutrons
together in its nucleus. It is the strongest known force in nature, but
is effective only over a short range.
The chemical properties of an atom depend mainly on the electrons in its outer shell or valence shell. If this shell is full, the atoms are called inert, or non-reactive. If it is partially filled an atom can enter a chemical reaction and form chemical bonds. Chemical bonds bind different elements tightly together in compounds. Both compounds and elements can exist as molecules, which are the smallest units of combined atoms with their own chemical identity.
When a Chemical Reaction occurs atoms gain, lose or share electrons. They always want to have their outer energy level full of electrons When an atom has a different number of protons & electrons it is called an ion. A positively charged ion has more protons than electrons A negatively charged ion has more electrons than protons.
There are four principal bonds between atoms: ionic, covalent, metallic, and hydrogen bonds.
Ionic, Covalent & Metallic Bonds
A Chemical Reaction happens whenever a chemical bond is formed or broken.
Reactants are the substances existing before the reaction. Products are the substances existing after the reaction. Catalysts are the substances that speed up the rate of a reaction.
Names & Symbols of Elements
Most Common Names and Symbols
Elements, Compounds & Mixtures
Elements in the Human Body
Molecular Structure & Moles
•Molecular weight is the sum of the weights of all the atoms in a molecule.
•A mole (mol) is equal in number to the molecular weight of a substance, but upscaled from daltons to units of grams.
Use the periodic table to calculate to molecular weight of each atom, and then add the totals together to get the mass of the molecule. Your answer should always contain the proper units, g/mol.
•One mole of sucrose weighs 342 g.
•12 x 12 g = 144 g/mol
•22 x ___ = ___
• 11 x ___ = ___
1.0 M solution would have 342 g of sucrose to 1 liter of water
One mole of ethyl alcohol (C2H6O) also contains 6.022 x 1023 molecules but weighs only 46g because the molecules are smaller.
Weight vs. Mass
An object's weight changes if the pull of gravity changes, but an object's mass is the same everywhere in the universe. If air resistance were not a factor, everything near the Earth's surface falls with acceleration g, so weight = mg.
Acid & Base Systems
Red Cabbage Indicator
The Chemistry of Carbon
Organic chemistry is the branch of chemistry dealing with the compounds of carbon. While it is only the fourteenth most common element on earth, carbon forms by far the greatest number of different compounds. Organic chemistry is of vital importance to the petrochemical, pharmaceutical, and textile industries, where a prime concern is the synthesis of new organic molecules and polymers.
Compounds containing only hydrogen and carbon are called hydrocarbons, the simplest is methane (CH4).
Testing for organic compounds in foods