Atom Molecule

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An atom is smallest particle in an element that has the properties of the element. It is not possible to breakdown the atom further retaining the properties of the element. Atoms are not visible to the naked eye and are the basic building blocks. For example the atoms of element gold cannot be broken down further and each atom has the properties of gold.

Have them predict whether each example is an atom or a molecule based on what they know. Label one side of your room 'atom' and one 'molecule'. Ask students to stand and walk to the side of the room for each molecule. Have students standing on the correct side tell why they chose that side. Atoms can bond together into groups and form a molecule. If the molecule contains atoms of different types bonded together, we call it a compound. For example, two hydrogen atoms and one oxygen.

An atom is the basic unit of an element. An atom is a form of matter which may not be further broken down using any chemical means. A typical atom consists of protons, neutrons, and electrons. An atom is the smallest particle of any element, whereas, a molecule is formed when two or more atoms are held together with the help of a chemical bond. It is possible for atoms to either exist or not exist independently. However, molecules always exist independently or in a free state. It is not possible to break down atoms any further. Summarized in Table 1. The protonis located in the center (or nucleus) of an atom, each atom has at least one proton. Protons have a charge of +1, and a mass of approximately 1 atomic mass unit (amu). Elements differ from each other in the number of protons they have, e.g.

Atom Molecule

Molecules are formed by the combination of two or more atoms. Unlike atoms, molecules can be subdivided to individual atoms. The atoms are bonded together in a molecule. Molecules also are not visible to the naked eye, while can be seen through highly magnifying microscopes and other scientific devices. Water is comprised of numerous water molecules. Each water molecule is made up of one oxygen atom and two hydrogen atoms. So a water molecule can be further divided into oxygen and hydrogen atoms. But these atoms cannot be subdivided. In a molecule, atoms are bonded together by single, double, or triple bonds.

An atom has a nucleus surrounded by electrons. The electrons are negatively charged particles. The nucleus contains neutrons and positively charged protons. Depending on the majority of the particles, the atom can be positively or negatively charged. When these charged atoms bond together to form molecules, the bonds are formed by the electrons filling up the outer orbits of the atoms. Since atoms exist independently, there is no bonding in an atom.

When atoms combine in different numbers to form a molecule, the end result can vary. For example, when two atoms of oxygen combine to form a molecule, it becomes O2 which is the oxygen we breathe in. But when three oxygen atoms combine to form an O3 molecule, it becomes Ozone. So another difference between atoms and molecules is that when similar atoms combine together in varying numbers, molecules of different properties can be formed. But when similar molecules combine together in any numbers, a simple product is formed.

Atom Molecule Definition

A molecule is usually stable to exist by itself but an atom is not stable by itself. This is owing to the presence of electrons in the atoms. Only when sufficient number of electrons are present in an atom, it becomes stable. The sufficient number of electrons are received in an atom, when two atoms bond together and share the electrons. Thus it becomes stable and forms a molecule. Not all atoms can bond together. The bonding depends on the charge and chemical properties of the atoms.

Atoms and molecules are present in all objects and living things. The composition and density levels vary the thickness and form of the objects. In gases, the molecules are very loosely packed so that the molecules can flow around easily without colliding. In liquids, the packing is a bit more compact and so the particles are always together. But in solids the packing is very compact and hardly any movement to the molecules is allowed, giving the object a firm shape.

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  • Atomic model
    • Basic properties
    • The electron
    • The nucleus
  • Development of atomic theory
    • The beginnings of modern atomic theory
    • Studies of the properties of atoms
    • Models of atomic structure
    • Advances in nuclear and subatomic physics
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Articles from Britannica Encyclopedias for elementary and high school students.
George F. BertschSee All Contributors
Professor of Physics, University of Washington, Seattle. Author of Oscillations in Finite Quantum Systems.

Atom, smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry.

Most of the atom is empty space. The rest consists of a positively charged nucleus of protons and neutrons surrounded by a cloud of negatively charged electrons. The nucleus is small and dense compared with the electrons, which are the lightest charged particles in nature. Electrons are attracted to any positive charge by their electric force; in an atom, electric forces bind the electrons to the nucleus.

Because of the nature of quantum mechanics, no single image has been entirely satisfactory at visualizing the atom’s various characteristics, which thus forces physicists to use complementary pictures of the atom to explain different properties. In some respects, the electrons in an atom behave like particles orbiting the nucleus. In others, the electrons behave like waves frozen in position around the nucleus. Such wave patterns, called orbitals, describe the distribution of individual electrons. The behaviour of an atom is strongly influenced by these orbital properties, and its chemical properties are determined by orbital groupings known as shells.

This article opens with a broad overview of the fundamental properties of the atom and its constituent particles and forces. Following this overview is a historical survey of the most influential concepts about the atom that have been formulated through the centuries. For additional information pertaining to nuclear structure and elementary particles, seesubatomic particles.

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Atomic model

Most matter consists of an agglomeration of molecules, which can be separated relatively easily. Molecules, in turn, are composed of atoms joined by chemical bonds that are more difficult to break. Each individual atom consists of smaller particles—namely, electrons and nuclei. These particles are electrically charged, and the electric forces on the charge are responsible for holding the atom together. Attempts to separate these smaller constituent particles require ever-increasing amounts of energy and result in the creation of new subatomic particles, many of which are charged.

As noted in the introduction to this article, an atom consists largely of empty space. The nucleus is the positively charged centre of an atom and contains most of its mass. It is composed of protons, which have a positive charge, and neutrons, which have no charge. Protons, neutrons, and the electrons surrounding them are long-lived particles present in all ordinary, naturally occurring atoms. Other subatomic particles may be found in association with these three types of particles. They can be created only with the addition of enormous amounts of energy, however, and are very short-lived.

All atoms are roughly the same size, whether they have 3 or 90 electrons. Approximately 50 million atoms of solid matter lined up in a row would measure 1 cm (0.4 inch). A convenient unit of length for measuring atomic sizes is the angstrom (Å), defined as 10−10 metre. The radius of an atom measures 1–2 Å. Compared with the overall size of the atom, the nucleus is even more minute. It is in the same proportion to the atom as a marble is to a football field. In volume the nucleus takes up only 10−14 metres of the space in the atom—i.e., 1 part in 100,000. A convenient unit of length for measuring nuclear sizes is the femtometre (fm), which equals 10−15 metre. The diameter of a nucleus depends on the number of particles it contains and ranges from about 4 fm for a light nucleus such as carbon to 15 fm for a heavy nucleus such as lead. In spite of the small size of the nucleus, virtually all the mass of the atom is concentrated there. The protons are massive, positively charged particles, whereas the neutrons have no charge and are slightly more massive than the protons. The fact that nuclei can have anywhere from 1 to nearly 300 protons and neutrons accounts for their wide variation in mass. The lightest nucleus, that of hydrogen, is 1,836 times more massive than an electron, while heavy nuclei are nearly 500,000 times more massive.

Atom Molecule Element

Basic properties

Atom Molecule Element Compound

Atomic number

Atom Molecule Matter

The single most important characteristic of an atom is its atomic number (usually denoted by the letter Z), which is defined as the number of units of positive charge (protons) in the nucleus. For example, if an atom has a Z of 6, it is carbon, while a Z of 92 corresponds to uranium. A neutral atom has an equal number of protons and electrons so that the positive and negative charges exactly balance. Since it is the electrons that determine how one atom interacts with another, in the end it is the number of protons in the nucleus that determines the chemical properties of an atom.

Atom Molecule Kit

Quick Facts

Difference Between Atom And Molecule

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