# What is the relationship between atomic number and density

### Phosphorus - Atomic Number - Atomic Mass - Density of Phosphorus - Nuclear Power

When you look at the structure of the atom, you have a dense, positive nucleus composed of protons and neutrons. Around the nucleus are a equal number of. The elements of the periodic table sorted by density. Atomic Number The first chemical element with the lowest density is Hydrogen and the highest Please note that the elements do not show their natural relation towards each other as. In physics, astronomy, chemistry, biology and geography, number density is an intensive 1 Definition; 2 Units; 3 Usage; 4 Relation to other quantities However, these units are not quite practical when dealing with atoms or molecules of.

The best we can do is to talk about the probability of finding an electron within a certain volume of space that surrounds the nucleus of the atom. Experimentally it is difficult to obtain isolated atoms. Hydrogen, for example, exists as a dinuclear compound rather than a mononuclear atom. While we can measure the "size" of this dinuclear compound, the relationship between its "size" and the radius of the mononuclear atom is not obvious. Since we can't be precise, the meaning of the term atomic radius is necessarily fuzzy.

Figure 1 shows the sizes of a select group of elements arranged according to their positions in the periodic table, i. The atomic radius, in picometers, is given below the sphere that represents the atom. The fuzziness of the edges of the spheres is meant to imply the uncertainty inherent in discussions of the size of an atom.

Figure 1 Atomic Radii as a Function of Atomic Number Before we consider the data in Figure 1, you may want to review your knowledge of the periodic table. Exercise 2 Across a given row of the periodic table, the general trend is that the radii of the atoms decrease as their atomic numbers. Such a relationship between atomic number and atomic radius is a direct correlation. According to Coulomb's Law, as the atomic number increases within a series of atoms, the nuclear attraction for electrons will also increase, thus pulling the electron s closer to the nucleus.

The Coulombic attraction of the nucleus of an atom for its electrons is referred to as the electronegativity of the atom. Exercise 3 Within a given group column of the periodic table, the general trend is that the radii of the atoms increase as their atomic numbers.

What's the Difference between Mass Number and Atomic Mass?

At this point we have an apparent dichotomy. On the one hand there is a direct correlation between atomic size and atomic number, while on the other there is an inverse correlation between these two variables.

Whenever you encounter a situation like this, you may be certain that there is another variable at play. You need more data. So let's look at Ionization Energies The ionization energy of an atom is the amount of energy required to separate an electron from the neutral atom. It is the energy needed to overcome the force of attaction, Fc, between the nucleus and the electron that is farthest from it. Equation 1 depicts the process in general terms.

Figure 2 presents a plot of ionization energies as a function of atomic number for the same elements shown in Figure 1. Across a given row of the periodic table, the general trend is that the ionization energies of the atoms increase as their atomic numbers.

Such a correlation between atomic number and ionization energy is direct inverse. Exercise 5 Complete the following statement: Within a given group column of the periodic table, the general trend is that the ionization energies of the atoms decrease as their atomic numbers. Let's think about what's involved in the measurement of the ionization energy of an atom. As Equation 1 indicates, the process requires the separation of an electron from the nucleus of an atom, i. According to Coulomb's Law, the ionization energies are a function of two variables, the atomic number and the atomic radius.

More importantly, these variables act in opposite directions on the ionization energies; an increase in atomic number should cause an increase in ionization energy, while an increase in atomic radius should result in a decrease.

The actual value of the ionization energy for a given atom will depend upon the balance of these two factors. Exercise 6 If q2 represents the charge on the electron, then the ionization energies should increase as the values of q1.

The data in Figure 2 indicate that this is always true generally true never true Before we proceed with our interpretation of the data in Figure 2, we need to take a closer look at Figure 1. Atomic mass The name indicates the mass of an atom, expressed in atomic mass units amu. Most of the mass of an atom is concentrated in the protons and neutrons contained in the nucleus.

Each proton or neutron weighs about 1 amu, and thus the atomic mass in always very close to the mass or nucleon number, which indicates the number of particles within the core of an atom; this means the protons and neutrons. Each isotope of a chemical element can vary in mass. The atomic mass of an isotope indicates the number of neutrons that are present within the core of the atoms.

The total atomic mass of an element is an equivalent of the mass units of its isotopes. The relative occurrence of the isotopes in nature is an important factor in the determination of the overall atomic mass of an element. In reference to a certain chemical element, the atomic mass as shown in the periodic table is the average atomic mass of all the chemical element's stable isotopes.

The average is weighted by the relative natural abundances of the element's isotopes. Electronegativity according to Pauling Electro negativity measures the inclination of an atom to pull the electronic cloud in its direction during chemical bonding with another atom. Pauling's scale is a widely used method to order chemical elements according to their electro negativity. Nobel prize winner Linus Pauling developed this scale in The values of electro negativity are not calculated, based on mathematical formula or a measurement.

It is more like a pragmatic range. Pauling gave the element with the highest possible electro negativity, fluorinea value of 4,0. Franciumthe element with the lowest possible electro negativity, was given a value of 0,7.

All of the remaining elements are given a value of somewhere between these two extremes.

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Density The density of an element indicates the number of units of mass of the element that are present in a certain volume of a medium. Traditionally, density is expressed through the Greek letter ro written as r. The density of an element is usually expressed graphically with temperatures and air pressures, because these two properties influence density.

The melting point of an element or compound means the temperatures at which the solid form of the element or compound is at equilibrium with the liquid form. We usually presume the air pressure to be 1 atmosphere.

### LON-CAPA PeriodicTable

The boiling point of an element or compound means the temperature at which the liquid form of an element or compound is at equilibrium with the gaseous form. At the boiling point the vapour pressure of an element or compound is 1 atmosphere.

Vanderwaals radius Even when two atoms that are near one another will not bind, they will still attract one another. This phenomenon is known as the Vanderwaals interaction. The Vanderwaals forces cause a force between the two atoms.

This force becomes stronger, as the atoms come closer together.

## Phosphorus – Atomic Number – Atomic Mass – Density of Phosphorus

However, when the two atoms draw too near each other a rejecting force will take action, as a consequence of the exceeding rejection between the negatively charged electrons of both atoms. As a result, a certain distance will develop between the two atoms, which is commonly known as the Vanderwaals radius.

Through comparison of Vanderwaals radiuses of several different pairs of atoms, we have developed a system of Vanderwaals radiuses, through which we can predict the Vanderwaals radius between two atoms, through addition. Ionic radius Ionic radius is the radius that an ion has in an ionic crystal, where the ions are packed together to a point where their outermost electronic orbitals are in contact with each other.

An orbital is the area around an atom where, according to orbital theory, the probability of finding an electron is the greatest. Isotopes The atomic number does not determine the number of neutrons in an atomic core. As a result, the number of neutrons within an atom can vary.

Then atoms that have the same atomic number may differ in atomic mass.