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❶Depending upon Your computer, You may be able to set Your browser s to reject cookies or delete cookies, but that may result in the loss of some functionality on the Website. In nuclear fission, a single large nucleus is divided into two or more smaller nuclei.

homework help model of an atom

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The word atom may also refer to the smallest possible indivisible fundamental particle. This definition must not be confused with that of chemical atoms, since chemical atoms are composed of smaller subatomic particles. Most atoms are composed of three types of subatomic particles which govern their external properties: Protons and neutrons are both nucleons and make up the dense, massive atomic nucleus.

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. Atoms are electrically neutral if they have an equal number of protons and electrons. Electrons that are furthest from the nucleus may be transferred to other nearby atoms or even shared between atoms. Atoms which have either a deficit or a surplus of electrons are called ions. The number of protons and neutrons in the atomic nucleus may also change, via nuclear fusion, nuclear fission or radioactive decay.

Atoms are the fundamental building blocks of chemistry, and are conserved in chemical reactions. Atoms are able to bond into molecules and other types of chemical compounds. Molecules are made up of multiple atoms; for example, a molecule of water is a combination of two hydrogen atoms and one oxygen atom. Contents 1 Properties of the atom 1. The first of these to be discovered was the negatively charged electron, which is easily ejected from atoms during ionization. The electrons orbit a small, dense body containing all of the positive charge in the atom, called the atomic nucleus.

This nucleus is itself made up of nucleons: Before , the subatomic particles were thought to consist of only protons, neutrons and electrons. However, protons and neutrons themselves are now known to consist of still smaller particles called quarks. In addition, the electron is known to have a nearly massless neutral partner called a neutrino. Together, the electron and neutrino are both leptons. Ordinary atoms are composed only of quarks and leptons of the first generation.

The proton is composed of two up quarks and one down quark, whereas the neutron is composed of one up quark and two down quarks.

Although they do not occur in ordinary matter, two other heavier generations of quarks and leptons may be generated in high-energy collisions. The subatomic force carrying particles called gauge bosons are also important to atoms. Electrons are bound to the nucleus by photons carrying the electromagnetic force. Protons and neutrons are bound together in the nucleus by gluons carrying the strong nuclear force. Electron configuration see main article electron configuration The chemical behavior of atoms is due to interactions between electrons.

Electrons of an atom remain within certain, predictable electron configurations. These configurations are determined by the quantum mechanics of electrons in the electric potential of the atom; the principal quantum number determines particular electron shells with distinct energy levels.

Generally, the higher the energy level of a shell, the further away it is from the nucleus. The electrons in the outermost shell, called the valence electrons, have the greatest influence on chemical behavior. Core electrons those not in the outer shell play a role, but it is usually in terms of a secondary effect due to screening of the positive charge in the atomic nucleus.

The atomic orbital wavefunctions of a hydrogen atom. The principal quantum number is at the right of each row and the azimuthal quantum number is denoted by letter at top of each column. An electron shell can hold up to 2n2 electrons, where n is the principal quantum number of the shell. The occupied shell of greatest n is the valence shell, even if it only has one electron.

Under some circumstances an electron may be excited to a higher energy level that is, it absorbs energy from an external source and leaps to a higher shell , leaving a space in a lower shell. In addition to its principal quantum number n, an electron is distinguished by three other quantum numbers: Electrons with varying l and m have distinctive shapes denoted by spectroscopic notation. In most atoms, orbitals of differing l are not exactly degenerate but separated into a fine structure.

Orbitals of differing m are degenerate but may be separated by applying a magnetic field, creating the Zeeman effect. Electrons with differing s have very slight energy differences called hyperfine splitting.

Nucleon properties The constituent protons and neutrons of the atomic nucleus are collectively called nucleons.

The nucleons are held together in the nucleus by the strong nuclear force. Nuclei can undergo transformations that affect the number of protons and neutrons they contain, a process called radioactive decay. When nuclei transformations take place spontaneously, this process is called radioactivity.

Radioactive transformations proceed by a wide variety of modes, but the most common are alpha decay emission of a helium nucleus and beta decay emission of an electron. Decays involving electrons or positrons are due to the weak nuclear interaction. In addition, like the electrons of the atom, the nucleons of nuclei may be pushed into excited states of higher energy.

However, these transitions typically require thousands of times more energy than electron excitations. When an excited nucleus emits a photon to return to the ground state, the photon has very high energy and is called a gamma ray.

Nuclear transformations also take place in nuclear reactions. In nuclear fusion, two light nuclei come together and merge into a single heavier nucleus. In nuclear fission, a single large nucleus is divided into two or more smaller nuclei.

Atom size and speed Atoms are much smaller than the wavelengths of light that human vision can detect, so atoms cannot be seen in any kind of optical microscope.

However, there are ways of detecting the positions of atoms on the surface of a solid or a thin film so as to obtain images. Since the electron cloud does not have a sharp cutoff, the size of an atom is not easily defined. For any atom, one might use the radius at which the electrons of the valence shell are most likely to be found. As an example, the size of a hydrogen atom is estimated to be approximately 1.

So the ratio of the size of the hydrogen atom to its nucleus is about , If an atom were the size of a stadium, the nucleus would be the size of a marble. Nearly all the mass of an atom is in its nucleus, yet almost all the space in an atom is filled by its electrons. Atoms of different elements do vary in size, but the sizes do not scale linearly with the mass of the atom.

Their sizes are roughly the same to within a factor of 2. The reason for this is that heavy elements have large positive charge on their nuclei, which strongly attract the electrons to the center of the atom.

This contracts the size of the electron shells, so that more electrons fit in the only a slightly greater volume. The temperature of a collection of atoms is a measure of the average energy of motion of those atoms; at 0 kelvins absolute zero atoms would have no motion.

As the temperature of the system is increased, the kinetic energy of the particles in the system is increased, and their speed of motion increases. Elements, isotopes and ions Atoms are generally classified by their atomic number Z, which corresponds to the number of protons in the atom. The atomic number determines which chemical element the atom is. For example, carbon atoms are atoms containing six protons. All atoms with the same atomic number share a wide variety of physical properties and exhibit the same chemical properties.

The elements may be sorted according to the periodic table in order of increasing atomic number. The atomic mass A, atomic mass number, or nucleon number of an element is the total number of protons and neutrons in an atom of that element, so-called because each proton and neutron has a mass of about 1 amu.

Each element can have numerous kinds of atoms with the same number of protons and electrons but varying numbers of neutrons. Each has the same atomic number but a different mass number. These are called the isotopes of an element. When writing the name of an isotope, the element name is followed by the mass number. For example, carbon contains 6 protons and 8 neutrons in each atom, for a total mass number of The atomic mass listed for each element in the periodic table is an average of the isotope masses found in nature, weighted by their abundance.

The simplest atom is the hydrogen isotope protium, which has atomic number 1 and atomic mass number 1; it consists of one proton and one electron. The hydrogen isotope which also contains one neutron so is called deuterium or hydrogen-2; the hydrogen isotope with two neutrons is called tritium or hydrogen Tritium is an unstable isotope which decays through a process called radioactivity. Almost all isotopes of each element are radioactive; only a few are stable. The elements with atomic number 84 polonium and heavier have no stable isotopes and are all radioactive.

Virtually all elements heavier than hydrogen and helium were created through stellar nucleosynthesis and supernova nucleosynthesis. Several elements that do not occur on Earth have been found to be present in stars. Elements not normally found in nature have been artificially created by nuclear bombardment; as of , elements have been created through atomic number given the temporary name ununhexium. These ultra-heavy elements are generally highly unstable and decay quickly.

Therefore, elements with the same number of valence electrons are grouped together in the columns of the periodic table of the elements. Alkali metals contain one electron on their outer shell; alkaline earth metals, two electrons; halogens, seven electrons; and various others. Every atom is most stable with a full valence shell. This means that atoms with full valence shells the noble gases are very unreactive.

Conversely, atoms with few electrons in their valence shell are more reactive. Alkali metals are therefore very reactive, with caesium, rubidium, and francium being the most reactive of all metals.

Also, atoms that need only few electrons such as the halogens to fill their valence shells are reactive. To re-enable the tools or to convert back to English, click "view original" on the Google Translate toolbar.

The number of protons always equals the number of electrons. Mass numbers of the isotopes are arranged in order of decreasing abundance. The same safe and trusted content for explorers of all ages. Accessible across all of today's devices: Improved homework resources designed to support a variety of curriculum subjects and standards.

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Homework Help Model Of An Atom. homework help model of an atom This is a homework activity in which students used the simulation to analyze the differences in the experimental predictions of each model of the atom and explain the reasoning behind the development of the models.

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Sep 03,  · This feature is not available right now. Please try again later. nuclear energy - The Bohr Model of the Hydrogen Atom - Bohr selected the hydrogen atom for study because it has the simplest atomic structure and its line spectrum could not be understood by earlier (classical) theories. As the single electron whirls around the nucleus, it is attracted to the nucleus by the electrostatic force of unlike charges.