It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements.
Summary
| Element | Helium |
| Atomic number | 2 |
| Atomic mass [amu] | 4.0026 |
| Atomic mass [pm] | 28 |
| Density at STP [g/cm3] | 0.00018 |
| Number of protons | 2 |
| Number of neutrons (typical isotopes) | 3; 4 |
| Number of electrons | 2 |
| Electron configuration | 1s2 |
| Oxidation states | 0 |
| Electron affinity [kJ/mol] | — |
| Electronegativity [Pauling scale] | — |
| First ionization energy [eV] | 24.5874 |
Atomic Number – Protons, Electrons and Neutrons in Helium
Heliumis a chemical element with atomic number2which means there are 2 protons in its nucleus. Total number of protons in the nucleus is called theatomic numberof the atom and is given thesymbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to1,602 x 10-19coulombs.
The total number ofneutronsin the nucleus of an atom is called theneutronnumberof the atom and is given thesymbol N. Neutronnumber plusatomic numberequals atomic mass number:N+Z=A. The difference between the neutron number and the atomic number is known as theneutron excess: D = N – Z = A – 2Z.
For stable elements, there is usually a variety of stable isotopes.Isotopesare nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons. Mass numbers of typical isotopes ofHeliumare3; 4.
Atomic Mass of Helium
Atomic mass ofHeliumis4.0026 u.
The atomic mass is the mass of an atom. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element. The atomic mass is carried by the atomic nucleus, which occupies only about 10-12of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total mass of the atom. Note that, eachelementmay contain moreisotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance.
Atomic Radius of Helium
The atomic radius ofHeliumatom is28pm(covalent radius).
It must be noted, atoms lack a well-defined outer boundary. The atomic radius of a chemical element is a measure of the distance out to which the electron cloud extends from the nucleus. However, this assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Therefore, there are various non-equivalent definitions of atomic radius.
Electrons and Electron Configuration
The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the number of electrons in neutral atom ofHeliumis2.Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
Since the number of electrons and their arrangement are responsible for the chemical behavior of atoms, theatomic numberidentifies the various chemical elements. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Electron configuration ofHeliumis1s2.
Possible oxidation states are0.
Density of Helium
DensityofHeliumis0.00018g/cm3.
Typical densities of various substances are at atmospheric pressure.
Densityis defined as themass per unit volume. It is anintensive property, which is mathematically defined as mass divided by volume:
ρ = m/V
Atomic Masses of Elements
Atomic Radii of Elements
Densities of Elements
Electron Affinity – Helium
Electron affinity ofHeliumis— kJ/mol.
In chemistry andatomic physics, theelectron affinityof an atom or molecule is defined as:
the change in energy (in kJ/mole) of a neutral atom or molecule (in the gaseous phase) when an electron is added to the atom to form a negative ion.
X + e–→ X–+ energy Affinity = – ∆H
In other words, it can be expressed as the neutral atom’slikelihood of gaining an electron. Note that, ionization energies measure the tendency of a neutral atom to resist the loss of electrons. Electron affinities are more difficult to measure than ionization energies.
Electronegativity of Helium
Electronegativity ofHeliumis—.
Electronegativity, symbol χ, is a chemical property that describes the tendency of an atom to attract electrons towards this atom. For this purposes, adimensionlessquantity thePauling scale, symbol χ, is the most commonly used.
The electronegativity of Helium is: χ = —
First Ionization Energy of Helium
First Ionization Energyof Helium is24.5874 eV.
Ionization energy, also calledionization potential, is the energy necessary toremove an electronfrom the neutral atom.
X + energy → X++ e−
where X is any atom or molecule capable of being ionized, X+is that atom or molecule with an electron removed (positive ion), and e−is the removed electron.
A Helium atom, for example, requires the following ionization energy to remove the outermost electron.
He + IE → He++ e− IE = 24.5874 eV
Electronegativity of Elements
Ionization Energy of Elements
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Properties of other elements
