First of all, you will come to the aid of the periodic table. Looking at her, you will see that each element has not only its own strictly defined place, but an individual serial number. For example, hydrogen it is equal to one, carbon – 6, gold – 79 and so on.
That is the sequence number describes the number of protons in the nucleus, that is, the positive charge of the nucleus of the atom. As the atom in the normal state is neutral, the positive charge must be balanced by a negative charge. Therefore, from hydrogen one electron, carbon, six electrons, gold has seventy – nine electrons.
But how to determine the number of electrons in the atom, if the atom, in turn, is part of a more complex molecule? For example, what is the number of electrons in the atoms of sodium and chlorine, if they form a molecule well known to all of you regular table salt?
And there's nothing difficult. Start with that, write a formula for this substance, it will be NaCl. From the formula you will see that a molecule of salt consists of two elements, namely the alkali metal sodium and the gas-halogen is chlorine. But this is not the neutral atoms of sodium and chlorine, and their ions. Chlorine, forming the ionic bond with sodium, thus "pulled" to one of its electrons, and sodium, respectively, it "gave".
Again, look at the periodic Table. You will see that sodium has a sequence number 11, chlorine is 17. Therefore, now the sodium ion will be 10 electrons, chlorine-ion – 18.
Acting according to the same algorithm, it is easy to determine the number of electrons in any chemical element, whether in the form of neutral atom or ion.
The proton is positively charged particles, neutrons do not carry any charge.
Advice 2: How to find the number of electrons in the atom
The atom consists of a nucleus and its surrounding electronsthat revolve around it for the atomic orbitals to form the electronic layers (energy levels). The number of negatively charged particles in external and internal levels determines the properties of the elements. The number of electronscontained in the atom, you find that knowing some key points.
You will need
- - handle;
- - periodic system.
To determine the number of electronsuse the periodic system of D. I. Mendeleev. In this table the elements are arranged in a sequence that is closely related to their atomic structure. Knowing that the positive charge of an atom is always equal to the sequence number of the element, you can easily find the number of negative particles. It is well known - the atom as a whole neutral, and therefore the number of electrons will equal the number of protons and the number of the element in the table. For example, the sequence number of aluminium is 13. Consequently, the number of electrons it will have a 13, sodium – 11, iron – 26, etc.
If you need to find the number of electrons in the energy levels, first follow the principle of Paul and the Hund rule. Then distribute the negative particle levels and sublevels with the same periodic system, and more precisely its periods and groups. So the number of the horizontal rows (period) indicates the number of layers of energy, and vertical (groups) on the number of electrons on the outer level.
Don't forget that the number of outer electrons equals the group number only elements that are in the main subgroups. The elements of side subgroups of the number of negatively charged particles at the last energy level may not be more than two. For example, scandium (Sc), 4 period, 3 group, side subgroup, their 2. In the Galia (Ga), which is in the same period and the same group, but in the main sub external electrons 3.
When counting electrons in the atom, please note that the last form molecules. The atoms may take, give negatively charged particles or to form a shared pair. For example, the hydrogen molecule (H2) a shared pair of electrons. Another case: in the molecule of sodium fluoride (NaF), the total sum of electrons is 20. But in the course of a chemical reaction the sodium atom gives up its electron and it is 10, and the fluorine takes - it turns out also 10.
Remember that on the outer energy level can only be 8 electrons. And it does not depend on the position of the element in the periodic table.