Periodic Table

An atom's reactivity depends on two main factors:

1. How many electrons it has in its valence shell. 2. How far those electrons are from the nucleus.

Below are shown some electron configurations. Which of these belongs to the atom that is most reactive? 2,8 / 2,8,1 / 2,8,2 / 2,8,2

2,8,1. The most reactive atom will be the one that can most easily gain a full electron shell. This is the one with the electron configuration 2,8,1. The atom with the full valence shell (2,8) is stable, so is not reactive. The atoms with 2 or 3 valence electrons are less reactive, because they need to lose more electrons in order to have a full valence shell and become stable.

State the number of valence electrons that the elements in group 17 have? Why?

7. The number of valence electrons an element has is equal to either the group number (groups 1 and 2) or the group number minus 10 (groups 13-18)

Why is hydrogen not classed as alkali metla?

Although hydrogen is technically in group 1, it is not classed as an alkali meal as it is has different properties to the other elements in this group.

Summarise how the elements are organised on the periodic table. In your answer, you should: State the order in which elements are placed in the table. Define period and group. Describe how the properties of the elements, and therefore their classification as a metal, non-metal or metalloid, changes as you move from left to rightacross the table.

Elements are placed in the periodic table in order of increasing atomic number. Elements were also initially placed in the same vertical column as other elements with similar chemical properties. We now know that this is because those elements have the same number of valence electrons, and therefore react in the same way. The vertical columns of the periodic table are called groups, while the horizontal rows are called periods. Moving across from left to right, elements go from metals to non-metals. Metals are found to the left and bottom of the periodic table. Non-metals are found at the top and right, while metalloids are found on the border between these two, and are often shown by a zig-zag line. Some properties of metals include: they are shiny, conduct electricity and heat, ductile and malleable, tend to have high melting points. Some properties of non-metals include: they are dull, poor conductors of electricity and heat, brittle, have low melting points.

Group 1 metals are ____reactive than group 1 metals, because only one valence electron must be ______ in order to achieve stability, compared to two electrons. This requires _____ and therefore the reactions of group 1 metals will be more vigorous.

Group 1 metals are more reactive than group 1 metals, because only one valence electron must be lost in order to achieve stability, compared to two electrons. This requires less energy and therefore the reactions of group 1 metals will be more vigorous.

Elements in group 16 of the periodic table are sometimes known as the chalcogens, although this name is not very common. Like the halogens, most of these elements are non-metals. Oxygen is a colourless gas at room temperature, sulfur is a yellow solid, and selenium is a red or grey solid.

In order to gain a full valence shell and become stable, group 16 elements need to gain two electrons. They are less reactive than the group 17 elements, because it is harder (requires more energy) to gain two electrons than to gain one electron to fill the valence shell.

Compare and contrast the reactivity and reactions of elements in the same group of the periodic table. Use the elements Mg, Ca, O and S to illustrate and explain your answer.

Moving down within the group, elements are involved in similar reactions since they all have the same number of valence electrons. For example, the electron configurations of the group 2 elements Mg and Ca are Mg 2, 8, 2 and Ca: 2, 8, 8, 2. Both have 2 valence electrons; therefore, are involved in similar reactions in order to lose these two electrons and become stable. The reactivity of the metals increases down the group since it is easier to lose the valence electrons as more energy levels are added to the atoms. The valence electrons are further from the nucleus, so it requires less energy to remove them from the valence shell. The reactions are faster and more violent moving down the group. O and S are also in the same group (16) and are involved in similar reactions to each other. The electron configurations of O and S are: (O: 2, 6 and S: 2, 8, 6). They both must gain 2 electrons to have a full shell, and so react in similar ways. Non-metals, such as O and S, get less reactive moving down the group because it is harder to gain electrons as more energy levels added to the atoms. The valence electrons are further from the nucleus, so it is more difficult to attract electrons into the valence shell.

As you move down a group, atoms have more electron shells and therefore the attractive force between the nucleus and the valence electrons decreases. What effect does this have on reactivity?

Reactivity increases down a group for metals; while reactivity decreases down a group for non-metals.

Elements in group 17 of the periodic table are known as the halogens. These elements are all non-metals. Fluorine and chlorine are both slightly yellow gases at room temperature, bromine is an orange liquid, and iodine is a purple-black solid.

The halogens are all very reactive. This is because they only need to gain one electron to fill their valence shell and become stable, which does not require much energy. Their reactivity means they are also very toxic, due to their ability to react with most of the chemical compounds in your body.

The metals in group 1 and 2 get _____ reactive as you move down the group. This is because the atoms get larger and the valence electrons are found _______the nucleus. The attractive force between the positively charged nucleus and the negatively charged valence electrons becomes _______, so it becomes easier to remove the valence electrons.

The metals in group 1 and 2 get more reactive as you move down the group. This is because the atoms get larger and the valence electrons are found further from the nucleus. The attractive force between the positively charged nucleus and the negatively charged valence electrons becomes weaker, so it becomes easier to remove the valence electrons.

An atom is stable, when it has a full valence electron shell. For the second and third electron shells, a full shell means it contains 8 electrons. Below are shown some electron configurations. Which of these belongs to the atom that is most reactive? 2,5 / 2,6 / 2,7 / 2,8

The most reactive atom will be the one that can most easily gain a full electron shell. This is the one with the electron configuration 2,7. The atom with the full valence shell (2,8) is stable, so it is not reactive. The atoms with 5 or 6 valence electrons are less reactive, because they need to gain more electrons in order to have a full valence shell and become stable.

What do elements in the same period in the periodic table have in common?

They have a similar size. They have the same number of electron shells.

What do elements in the same group on the periodic table have in common?

They have the same number of valence electrons. They have similar chemical reactivity.

Elements in group 1 of the periodic table are known as

alkali metals

Moving down a group, atoms have more electron shells and therefore the attractive force between the nucleus and valence electrons _______

decreases

Atoms without full valence shells usually react with other atoms by

gaining, losing or sharing electrons in chemical bonds in order to achieve stability.

Non metals tend to have a ____numbers of valence electrons

high numbers

Atoms with full valence electron shells are said to be

stable, which means they do not react with other atoms

The outer electron shell (energy level) of an atom is called the valence shell.

the valence shell.

the further from the nucleus the valence electrons are, the _______ the attractive force between the nucleus and valence electrons.

weaker the attractive force between the nucleus and valence electrons.