Chapter 2. Basic Chemistry
2.1 Chemical elements
- Matter refers to anything that takes up space and has mass. It is helpful to remember that matter can exist as a solid, a liquid, or a gas.
- All matter is composed of certain basic substances called elements.
- A property is a physical or chemical characteristic, such as density, solubility, melting point, and reactivity.
- Six elements—carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur make up most of the body weight of organisms.
Atomic structure
- Elements consist of tiny particles called atoms.
- One or two litters create the atomic symbol, which stands for this name.
- The mass number of atom is in turn dependent upon the presence of certain subatomic particles. Protons, neutrons, and electrons.
- All atoms of an element have the same number of protons. This is called the atom’s atomic number.
- This is what makes an atom unique.
The periodic Table
- The vertical columns in the table are groups; the horizontal rows are period that cause each atom to be in a particular group.
- The atomic number is above the atomic symbol and the mass number is below the atomic symbol.
Isotopes
- Isotopes are atoms of the same element that differ in the number of neutrons. In other words, isotopes have the same number of protons but they have different mass numbers.
- The chemical behavior of a radioactive isotope is essentially the same as that of the stable isotopes of an element.
- Radioactive substances in the environment can harm cells, damage DNA, and cause cancer.
Electrons and energy
- An orbital is defined as a particular volume of space where an electron is most apt to be found most of the time.
- The octet rule, states that the outer shell is most stable when it has eight electrons, hold.
2.2 Elements and Compounds.
- Atoms except for noble gases, routinely bond with one another.
- When atoms of two or more different elements bond together, the product is called a compound.
Ionic Bonding
- Ions form when electrons are transferred from one atom to another.
- This election transfer causes a charge imbalance in each atom. Therefore, it has a net of charges
- Ionic compounds are held together by an attraction between negatively and positively charged ions called an ionic bond.
- Salts can exist as a dry solid, but when salts are placed in water, they release ions as they dissolve.
Covalent Bonding
- A covalent bond results when two atoms share electrons in such a way that each atom has an octet of electrons in the other shell
- When the sharing of electrons between two atoms is fairly equal, the covalent bond is said to be a nonpolar covalent bond.
- The attraction of an atom for the electrons in a covalent bond is called its electro negativity.
- The unequal sharing of electrons in a covalent bond creates a polar covalent bond.
- Polarity within a water molecule causes the hydrogen atoms in one molecule to be attracted to the oxygen atoms in other water molecules. This attraction, although weaker than an ionic or covalent bond, is called a hydrogen bond. More easily broken.
- Hydrogen bonds between parts of cellular molecules help maintain their proper structure and function.
2.3 Chemistry of Water
- Properties of water
a. Water has a high heat capacity
b. Water has a high heat of vaporization.
c. Water is a solvent
d. Water molecules are cohesive and adhesive
e. Water has a high surface tension
f. Unlike most substances, frozen water is less dense than liquid water.