atom (redirected from Structure of the atom)

atom /at·om/ (at´om) the smallest particle of an element with all the properties of the element; it consists of a positively charged nucleus (made up of protons and neutrons) and negatively charged electrons, which move in orbits about the nucleus.atom´ic

---

at·om (tm)

n.

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.

2. This unit regarded as a source of nuclear energy.

3. A part or particle considered to be an irreducible constituent of a specified system.

4. The irreducible, indestructible material unit postulated by ancient atomism.

5. An extremely small part, quantity, or amount.

---

a·tomic (-tmk) adj.

---

atom

[at′əm]

Etymology: Gk, atmos, indivisible

1 (in chemistry and physics) the smallest division of an element that exhibits all the properties and characteristics of the element. It comprises neutrons, electrons, and protons. The number of protons in the nucleus of every atom of any given element is the same and is called its atomic number.

2 

Usage notes: nontechnical,

the amount of any substance that is so small that further division is not possible. atomic, adj.

---

atom,

n the smallest component of an element that retains the element's chemical properties. Atoms comprise molecules and are themselves divisible into electrons, neutrons, and protons.

---

atom (at´m),

n the smallest part of an element capable of entering into a chemical reaction.

---

atom

the smallest particle of an element that has all the properties of the element.

There are two main parts of an atom: the nucleus and the electron cloud. The nucleus is made up of protons, which carry a positive electrical charge, and (except in hydrogen) neutrons, which contain one proton and one electron and carry no electrical charge. The electron cloud is made up of particles called electrons, which carry a negative electrical charge and move in orbits or 'shells' around the nucleus. Different atoms have different numbers of protons, neutrons and electrons in their makeup.

The atomic number of an element is the number of free protons (those not in neutrons) in the nucleus; it is equal to the net positive charge of the nucleus.

The atomic weight is the weight of an atom of a substance as compared with the weight of an atom of carbon-12, which is taken as 12.