# Hydrogen Valence Electrons

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1. You can find out how many valance electrons an element has by looking at the group number of the element on the periodic table. Well neon and helium are noble gases and are in group 8 and have 8 valence electrons. Bromine is in group 7 so it has 7 valence electrons magnesium is in group 2 so it has 2 valence electrons.
2. Helium and hydrogen have no inner electrons to shield the kernel and their 1s orbitals are smaller, compared to respective higher s orbitals So their ionization energy, especially for helium, is high, and reactivity reciprocally low.

### Learning Objectives

Hydrogen has 1 valence electron and Iodine (in Group 7 with F and Cl) has 7 valence electrons. With the Lewis Structure for HI remember that Hydrogen only needs 2 valence electrons to have a full outer shell. Be sure that you don’t use more than the 8 valence electrons available. HI Lewis Structure - How to Draw the Dot Structure for HI. Formal Charge = # valence electrons on neutral atom – (# lone electron pairs) + (½ # bonding electrons) Valence electrons = corresponds to the group number of the periodic table (for representative elements). Lone Pairs = lone electrons sitting on the atom. Each electron counts as one and so a.

• Define Lewis electron-dot structure.
• Define single covalent bond.
• Define structural formula.

### What does cholesterol really look like?

We can write the structure of the cholesterol molecule a couple of different ways. The simplest approach is to just write C27H46O. This “structure” is not very useful because it does not tell us how the carbons, hydrogens, and oxygen are connected to one another.

The structure in the figure to the right is much more helpful—in it, we can see how the different atoms are connected together to form the molecule.

In a previous chapter, you learned that the valence electrons of an atom can be shown in a simple way with an electron dot diagram. A hydrogen atom is shown as H• because of its one valence electron. The structures of molecules that are held together by covalent bonds can be diagrammed by Lewis electron-dot structures . The hydrogen molecule is shown in the Figure 1.

Figure 1. On the left is a single hydrogen atom with one electron. On the right is an H2 molecule showing the electron cloud overlap.

The shared pair of electrons is shown as two dots in between the two H symbols (H:H). This is called a single covalent bond, when two atoms are joined by the sharing of one pair of electrons. The single covalent bond can also be shown by a dash in between the two symbols (H–H). A structural formula is a formula that shows the arrangement of atoms in a molecule and represents covalent bonds between atoms by dashes.

## The Octet Rule and Covalent Bonds

When ions form, they conform to the octet rule by either losing or gaining electrons in order to achieve the electron configuration of the nearest noble gas. In a similar way, nonmetal atoms share electrons in the formation of a covalent in bond such a way that each of the atoms involved in the bond can attain a noble-gas electron configuration. The shared electrons are “counted” for each of the atoms involved in the sharing. For hydrogen (H2), the shared pair of electrons means that each of the atoms is able to attain the electron configuration of helium, the noble gas with two electrons. For atoms other than hydrogen, the sharing of electrons will usually provide each of the atoms with eight valence electrons.

### Summary

• Lewis electron-dot structures show the bonding in covalent molecules.
• Covalent bonds between atoms can be indicated either with dots (:) or a dash (-).

### Practice

Use the link below to answer the following questions:

1. Who developed the electron-dot structure system?
2. Are lines or dots more commonly used?
3. How are unbounded electrons represented?
4. Which atom is selected as the central atom?

### Review

1. What is a single covalent bond?
2. How can covalently-bound atoms obey the octet rule?
3. Does the hydrogen molecule obey the octet rule?

## Glossary

### Hydrogen Valence Electrons Atoms

• Lewis electron-dot structures: A way of representing covalent bonds in molecules.
• octet rule: Ions form by adding or losing electrons to form an outer shell of eight.
• single covalent bond: When two atoms are joined by the sharing of one pair of electrons.
• structural formula: A formula that shows the arrangement of atoms in a molecule and represents covalent bonds between atoms by dashes.
Show References

## References

### Hydrogen Valence Electrons Outer Shell

1. User:BorisTM/Wikimedia Commons.http://commons.wikimedia.org/wiki/File:Cholesterol.svg .
2. CK-12 Foundation – Jodi So.

You probably think of water as a substance that can put out fires. But some elements are so reactive that they burn in water. In fact, they virtually explode in water. An example is shown in the photo below. About 3 pounds of sodium were added to water, and the result was an explosive reaction. Why is sodium such a reactive element? In this section, you will find out.

## The First Group

Sodium (left( ce{Na} right)) is an element in group 1 of the periodic table of the elements. This group (column) of the table is shown below. It includes the nonmetal hydrogen (left( ce{H} right)) and six metals called alkali metals. Elements in the same group of the periodic table have the same number of valence electrons. These are the electrons in the outer energy level of the atoms that can be involved in chemical reactions. Valence electrons determine many of the properties of an element, so elements in the same group have similar properties. All the elements in group 1 have just one valence electron. This makes them very reactive.

## Reactivity of Group 1 Elements

Hydrogen is a very reactive gas, and the alkali metals are even more reactive. In fact, they are the most reactive metals and, along with the elements in group 17, are the most reactive of all elements. The reactivity of alkali metals increases from the top to the bottom of the group, so lithium (left( ce{Li} right)) is the least reactive alkali metal and francium (left( ce{Fr} right)) is the most reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with group 17 elements, which are very 'eager' to gain an electron.

## Other Properties of Alkali Metals

Besides being very reactive, alkali metals share a number of other properties:

• Alkali metals are all solids at room temperature.
• Alkali metals are low in density, and some of them float on water.
• Alkali metals are relatively soft. Some are even soft enough to cut with a knife, like the sodium pictured in the figure below.

## A Closer Look

Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another.

## Summary

• Group 1 of the periodic table includes hydrogen and the alkali metals.
• Because they have just one valence electron, group 1 elements are very reactive. As a result, they are found in nature only in combination with other elements.
• Alkali metals are all solids at room temperature. They are relatively soft and low in density.
• From the top to the bottom of group 1, the elements have heavier, more reactive atoms.

## Explore More

At the following URL, click on 'Group 1 data and graphs'. Use the data in the group 1 table to fill in the blanks below with either increases or decreases.

From the top to the bottom of group 1, properties of the alkali metals change as follows:

1. Melting point _________.

2. Boiling point _________.

### Hydrogen Valence Electrons Number

3. Density _________.

4. Atomic radius _________.

5. Number of electrons _________.

## Contributors and Attributions

• CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.