2. Chemistry comes alive 2.1- 2.2

Summarizing

2.1 Matter is the stuff of the universe and energy moves matter and 2.2 the properties of an element depend on the structure of its atoms.

Using mass number notation, we can identify the number of protons, electrons, and neutrons.

Using mass number notation allows us to deduce the total number and kinds of subatomic particles in any atom because it indicates the number of protons(the atomic number), the number of electrons(equal to the atomic number) and the number of neutrons(mass number minus atomic number).

Atomic weight is the average of the mass numbers of the isotopes of an element.

The atomic number of any atom is equal to the number of protons in its nucleus and is written as a subscript to the left of its atomic symbol.

Electrical energy is represented by the flow of charged particles along a conductor or the flow of ions across a membrane.

Electrical energy results from the movement of charged particles. In your home, electrical energy is found in the flow of electrons along the household wiring. In your body, electrical currents are generated when charged particles called ions move along or across cell membranes.

The nervous system uses electrical currents, called nerve impulses, to transmit messages from one part of the body to another.

Electrical currents travelling across the heart stimulate it to contract(beat) and pump blood(this is why a strong electrical shock, which interferes with such currents, can cause death).

Mechanical energy is energy directly involved in moving matter. When you ride a bicycle, your legs provide the mechanical energy that moves the pedals.

Radiant energy or electromagnetic radiation is energy that travels in waves. These waves, which vary in length, are collectively called the electromagnetic spectrum. They include visible light infrared waves, radio waves, ultraviolet waves and x-rays.

Light energy which stimulates the retinas of our eyes is important in vision.

Ultraviolet waves cause sunburn, but they also stimulate your body to make vitamin D.

Energy exists in two states, and each can be transformed to the other.

Kinetic energy is energy in action. we see evidence of kinetic energy in the constant movement of the tiniest particles of matter(atoms) as well as in large objects(a bouncing ball).

Kinetic energy does work by moving objects, which in turn can do work by moving or pushing on other objects. For example, a push on a swinging door sets it into motion.

proton - 양성자	electron - 전자	neutron - 중성자
particle -입자	atom - 원자	isotope - 동위 원소
mechanical energy - 역학 에너지	kinetic energy - 운동 에너지	electromagnetic spectrum - 전자기 스펙트럼

Potential energy is stored energy, that is, inactive energy that has the potential or capability to do work but is not presently doing so.

The batteries in an unused toy have potential energy, as does water confined behind a dam. Your leg muscles have potential energy when you sit still on the couch. When potential energy is released, it becomes kinetic energy and so is capable of doing work. For example, dammed water becomes a rushing torrent when the dam is opened, and that rushing torrent can move a turbine at a hydroelectric plant, or charge a battery.

Carbon, oxygen, hydrogen and nitrogen make up about 96% of body weight and 20 others are present in the body.

Chemical energy in the form of ATP is the most useful form of energy in living systems because it is used to run almost all functional processes.

Chemical energy is the form stored in the bonds of chemical substances. When chemical reactions occur that rearrange the atoms of the chemicals in a certain way, the potential energy is unleashed and becomes kinetic energy or energy in action. For example, some of the energy in the foods you eat is eventually converted into the kinetic energy of your moving arm. However, food fuels cannot be used to energize the body activities directly. Instead, some of the food energy is captured temporarily in the bonds of a chemical called adenosine triphosphate(ATP). Later, ATP's bonds are broken and the stored energy is released as needed to do cellular work. Chemical energy in the form of ATP is the most useful form of energy in living systems because it is used to run almost all functional processes.

The number of protons is always equal to the number of electrons in an atom, so the atomic number indirectly tells us the number of electrons in the atom. This information is important because electrons determine the chemical behavior of atoms.

The mass number of an atom is the sum of the masses of its protons and neutrons. The mass of the electrons is so small that it is ignored.

The atomic weight is an average of the relative weights(mass numbers) of all the isotopes of an element taking into account their relative abundance in nature. Protons and neutrons are heavy particles and have approximately the same mass, arbitrarily designated as 1 atomic mass unit.

The heavier isotopes of many elements are unstable, and their atoms decompose spontaneously into more stable forms. This process of atomic decay is called radioactivity and isotopes that exhibit this behavior are call radioisotopes.

decay - 부패, 부식

radioactivity - 방사능(성)

radioisotope - 방사선 동위원소

Radiant energy is energy that travels in waves.

Kinetic energy is energy in action.

Potential energy can be converted to kinetic energy.

The atomic number determines the number of protons in an atom.

The mass number indicates the total masses of the protons and neutrons present in the nucleus of the atom. Each proton and neutron has a mass of 1 atomic mass unit(amu). Therefore, an atom with mass number of 14 amu would have 6 protons and (14-6) 8 neutrons.

Matter is anything that occupies space and has mass with some exceptions, it can be seen, smelled and felt. The mass of an object is equal to the actual amount of matter in the object and it remains constant wherever the object is. In contrast, weigh varies with gravity.

All matter is composed of elements, unique substances that cannot be broken down into simpler substances by ordinary chemical methods. Among the well-known elements are oxygen, carbon, gold, silver, copper and iron. At present, 118 elements are recognized of these, 92 occur in nature, the rest are made artificially in particle accelerator devices.

Some common compounds, not elements are salt, acid, and water.

Protons and neutrons are heavy particles and have approximately the same mass, arbitrarily designated as 1 atomic mass unit(1 amu). Since all of the heavy subatomic particles are concentrated in the nucleus, the nucleus is fantastically dense, accounting for nearly the entire mass(99.9%) of the atom.

An electron has only about 1/2000 the mass of a proton and the mass of an electron is usually designated as 0 amu.