define atom?

Answer 1

A unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. The entire structure has an approximate diameter of 10-8 centimeter and characteristically remains undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons.

Answer 2

the smallest component of an element having the chemical properties of the element

is the smallest possible particle of a chemical element that retains its chemical properties. The word atom originally meant the smallest possible indivisible particle, but after the term came to have a specific meaning in science, atoms were found to be divisible and composed of smaller subatomic particles.

Most atoms are composed of three types of subatomic particles which govern their external properties:

electrons, which have a negative charge and are the least massive of the three;
protons, which have a positive charge and are about 1836 times more massive than electrons; and
neutrons, which have no charge and are about 1839 times more massive than electrons.
Protons and neutrons make up a dense, massive atomic nucleus, and are collectively called nucleons. The electrons form the much larger electron cloud surrounding the nucleus.

Atoms differ in the number of each of the subatomic particles they contain. The number of protons in an atom (called the atomic number) determines the element of the atom. Within a single element, the number of neutrons may also vary, determining the isotope of that element. The number of protons and neutrons in the atomic nucleus may also change, via nuclear fusion, nuclear fission or radioactive decay. The number of electrons associated with an atom is most easily changed, due to the lower energy of binding of electrons.

Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms which have either a deficit or a surplus of electrons are called ions. Electrons that are furthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism atoms are able to bond into molecules and other types of chemical compounds like ionic crystals. Molecules are the smallest division of a general collection of matter, including chemical compounds, which retains chemical properties. Most molecules are made up of multiple atoms; for example, a molecule of water is a combination of two hydrogen atoms and one oxygen atom. A few types of molecules (for example gas molecules of elements that do not form compounds, such as helium) are composed of only a single atom.

Atoms are the fundamental building blocks of chemistry, and are conserved in chemical reactions

Answer 3

a. A part or particle considered to be an irreducible constituent of a specified system.
b. The irreducible, indestructible material unit postulated by ancient atomism.
2. An extremely small part, quantity, or amount.
3. Physics & Chemistry
a. A unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. The entire structure has an approximate diameter of 10-8 centimeter and characteristically remains undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons.
b. This unit regarded as a source of nuclear energy.
Source: www.thefreedictionary.com/atom

Answer 4

Atoms are the basic building blocks of matter that make up everyday objects. A desk, the air, even you are made up of atoms!

There are 90 naturally occurring kinds of atoms. Scientists in labs have been able to make about 25 more.

Atoms are made out of three basic particles:
-Protons - carry a positive charge
-Neutrons - carry a negative charge
(Protons and Neutrons join together to form the nucleus - the central part of the atom.)
-Electrons - carry a negative charge and circle the nucleus

Answer 5

The basic component of all matter. The atom is the smallest particle of an element that has all of the chemical properties of that element. Atoms consist of a nucleus of protons and neutrons surrounded by electrons.

Answer 6

An atom is a particle of matter that uniquely defines a chemical element. An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons.

A proton is positively charged. The number of protons in the nucleus of an atom is the atomic number for the chemical element. A proton has a rest mass, denoted mp, of approximately 1.673 x 10-27 kilogram (kg). A neutron is electrically neutral and has a rest mass, denoted mn, of approximately 1.675 x 10-27 kg. The mass of a proton or neutron increases when the particle attains extreme speed, for example in a cyclotron or linear accelerator.

An early model of the atom was developed by the physicist Ernest Rutherford in 1912. He was the first to suggest that atoms are like miniature solar systems, except that the attractive force is not caused by gravity, but by opposing electrical charges. In the so-called Rutherford atom, electrons orbit the nucleus in circular paths. Niels Bohr revised Rutherford's theory in 1913. In the Bohr atom, the negatively charged electrons orbit the nucleus at specific median distances. These distances are represented by spheres, called shells, surrounding the nucleus. Electrons can move from shell to shell. When an electron absorbs enough energy, it moves to a larger, or higher, shell. When it loses a certain amount of energy, it falls to a smaller, or lower, shell.

The total mass of an atom, including the protons, neutrons and electrons, is the atomic mass or atomic weight. Electrons contribute only a tiny part of this mass. For most practical purposes, the atomic weight can be thought of as the number of protons plus the number of neutrons. Because the number of neutrons in an atom can vary, there can be several different atomic weights for most elements.

Atoms having the same number of protons, but different numbers of neutrons, represent the same element, but are known as different isotopes of that element. The isotope for an element is specified by the sum of the number of protons and neutrons. Examples of different isotopes of an element are carbon 12 (the most common, non-radioactive isotope of carbon) and carbon 14 (a less common, radioactive isotope of carbon).

Protons and electrons have equal and opposite charge, and normally an atom has equal numbers of both. Thus, atoms are usually neutral. An ion is an atom with extra electrons or with a deficiency of electrons, resulting in its being electrically charged. An ion with extra electrons is negatively charged and is called an anion; an ion deficient in electrons is positively charged and is called a cation.

Answer 7

Atom is the basic unit of chemical element. An atom , roughly 10cm in diameter, consists of a tiny, dense,positively charged nucleus made of neutrons and protons, surrounded by a cloud of negatively charged electrons. Each chemical element consists of atoms that posses a characteristic number of protons. Atom are held together in molecules by sharing electrons.

Answer 8

Atom is a simple way to read and write information on the web, allowing you to easily keep track of more sites in less time, and to seamlessly share your words and ideas by publishing to the web.

If you're new to Atom, you can find out more about what Atom can do for you. Or if you just want to get started, tools and services which work with the Atom format are listed in the AtomEnabled directory.

Created by leading service providers, tool vendors and independent developers, Atom is designed to be a universal publishing standard for personal content and weblogs. Technical information about working with the Atom format is available at the developer information page, and publications or weblogs that are interested in the benefits of being AtomEnabled can find out more about the benefits of Atom for publishers.

Answer 9

A part or particle considered to be an irreducible constituent of a specified system.
The irreducible, indestructible material unit postulated by ancient atomism.
An extremely small part, quantity, or amount.
Physics & Chemistry
A unit of matter, the smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. The entire structure has an approximate diameter of 10-8 centimeter and characteristically remains undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons.
This unit regarded as a source of nuclear energy. See Table at subatomic particle.

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ETYMOLOGY:
Middle English attome, from Latin atomus, from Greek atomos, indivisible, atom : a-, not ; see a- 1 + tomos, cutting (from temnein, to cut; see tem- in Indo-European

Answer 10

In chemistry and physics, an atom (Greek άτομον meaning "indivisible") is the smallest possible particle of a chemical element that retains its chemical properties. The word atom originally meant the smallest possible indivisible particle, but after the term came to have a specific meaning in science, atoms were found to be divisible and composed of smaller subatomic particles.