economic english 8 ppt

Elements that share the same period have the same num￾ber of electron shells.

Common Elements

Some elements are frequently encountered in biologi￾cally important molecules and everyday life. Below you

will find a list of common elements, their symbols, and

common uses.

H—Hydrogen: involved in the nuclear process that

produces energy in the sun

He—Helium: used to make balloons fly

C—Carbon: found in all living organisms; pure car￾bon exists as graphite and diamonds

N—Nitrogen: used as a coolant to rapidly freeze

food

O—Oxygen: essential for respiration (breathing)

and combustion (burning)

Si—Silicon: used in making transistors and solar

cells

Cl—Chlorine: used as a disinfectant in pools and as

a cleaning agent in bleach

Ca—Calcium: necessary for bone formation

Fe—Iron: used as a building material; carries oxygen

in the blood

Cu—Copper: a U.S. penny is made of copper; good

conductor of electricity

I—Iodine: lack in the diet results in an enlarged thy￾roid gland, or goiter

Hg—Mercury: used in thermometers; ingestion can

cause brain damage and poisoning

Pb—Lead: used for X-ray shielding in a dentist

office

Some elements exist in diatomic form (two atoms of

such an element are bonded), and are technically mole￾cules. These elements include hydrogen (H2), nitrogen

(N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine

(Br2), and iodine (I2).

Structure and Properties

of Matter

Matter has weight and takes up space. The building

blocks of matter are atoms and molecules. Matter can

interact with other matter and with energy. These inter￾actions form the basis of chemical and physical

reactions.

Molecules

Molecules are composed of two or more atoms. Atoms

are held together in molecules by chemical bonds.

Chemical bonds can be ionic or covalent. Ionic bonds

form when one atom donates one or more electrons to

another. Covalent bonds form when electrons are shared

between atoms. The mass of a molecule can be calculated

by adding the masses of the atoms of which it is com￾posed. The number of atoms of a given element in a

molecule is designated in a chemical formula by a sub￾script after the symbol for that element. For example, the

glucose (blood sugar) molecule is represented as

C6H12O6. This formula tells you that the glucose mole￾cule is contains six carbon atoms (C), twelve hydrogen

atoms (H), and six oxygen atoms (O).

Organic and Inorganic Molecules

Molecules are often classified as organic or inorganic.

Organic molecules are those that contain both carbon

and hydrogen. Examples of organic compounds are

methane (natural gas, CH4), glycine (an amino acid,

NH2CH2COOH), and ethanol (an alcohol, C2H5OH).

Inorganic compounds include sodium chloride (table

salt, NaCl), carbon dioxide (CO2), and water (H2O).

States of Matter

Matter is held together by intermolecular forces—forces

between different molecules. Three common states of

matter are solid, liquid, and gas. Matter is an atom, a

molecule (compound), or a mixture. Examples of mat￾ter in solid form are diamonds (carbon atoms), ice

(water molecules), and metal alloys (mixtures of differ￾ent metals). A solid has a fixed shape and a fixed volume.

The molecules in a solid have a regular, ordered arrange￾ment and vibrate in place, but are unable to move far.

Examples of matter in liquid form are mercury (mer￾cury atoms), vinegar (molecules of acetic acid), and per￾fume (a mixture of liquids made of different molecules).

Liquids have a fixed volume, but take the shape of the

container they are in. Liquids flow, and their density

(mass per unit volume) is usually lower than the density

of solids. The molecules in a liquid are not ordered and

can move by sliding past one another through a process

called diffusion.

–PHYSICAL SCIENCE–

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