And to get things in the right order for our shells, let me put the 3d1 before the 4s2. And so when people think about the aufbau principle, they imagine all of these d-block elements as somehow filling the d-block. Now as we know in other videos, that's not exactly true, but when you're conceptualizing the electron configuration it might be useful.
Then you come over here and you start filling the p-block. So for example, if you look at the electron configuration for, let's say carbon, carbon is going to have the same electron configuration as helium, as helium, and then you're going to fill your s-block 2s2, and then 2p one 2. So 2p2. So how many valence electrons does it have? Well, in its second shell, its outermost shell, it has two plus two, it has four valence electrons, and that's going to be true for the things in this group, and because of that, carbon has similar bonding behavior to silicon, to the other things in its group.
And we can keep going on, you know, for example, oxygen, oxygen and sulfur, these would both want to take two electrons from someone else because they have six valence electrons, they want to get to eight, so they have similar bonding behavior. You go to this yellow group right over here, these are the halogens. So there's a special name for them. These are the halogens. And these are highly reactive, because they have seven valence electrons.
They would love nothing more than to get one more valence electron, so they love to react, in fact, they especially love to react with the alkali metals over here. And then finally, you get to kind of your atomic nirvana in the noble gases here. And so the noble gases, that's the other name for the group 18 elements, noble gases. And they all have the very similar property of not being reactive. Why don't they react? They have filled their outermost shell. They don't find the need, they're noble, they're kind of above the fray, they don't find the need to have to react with anyone else.
Understand: the periodic table and properties of elements. The periodic table is an arrangement of the elements in order of their atomic numbers so that elements with similar properties appear in the same vertical column or group. The figure below shows the most commonly used form of the periodic table. Each square shows the chemical symbol of the element along with its name. Notice that several of the symbols seem to be unrelated to the name of the element: Fe for iron, Pb for lead, etc.
Most of these are the elements that have been known since ancient times and have symbols based on their Latin names. The atomic number of each element is written above the symbol. A period is a horizontal row of the periodic table. There are seven periods in the periodic table, with each one beginning at the far left. A new period begins when a new principal energy level begins filling with electrons. Period 1 has only two elements hydrogen and helium , while periods 2 and 3 have 8 elements. Periods 4 and 5 have 18 elements.
Periods 6 and 7 have 32 elements because the two bottom rows that are separated from the rest of the table belong to those periods. They are pulled out in order to make the table itself fit more easily onto a single page.
A group is a vertical column of the periodic table, based on the organization of the outer shell electrons. They are also extremely reactive and will burst into flame or even explode on contact with water, so chemists store them in oils or inert gases.
Hydrogen, with its single electron, also lives in Group 1, but the gas is considered a nonmetal. Alkaline-earth metals: The alkaline-earth metals make up Group 2 of the periodic table, from beryllium Be through radium Ra.
Each of these elements has two electrons in its outermost energy level, which makes the alkaline earths reactive enough that they're rarely found alone in nature. But they're not as reactive as the alkali metals. Their chemical reactions typically occur more slowly and produce less heat compared to the alkali metals. Lanthanides: The third group is much too long to fit into the third column, so it is broken out and flipped sideways to become the top row of the island that floats at the bottom of the table.
This is the lanthanides, elements 57 through 71 — lanthanum La to lutetium Lu. The elements in this group have a silvery white color and tarnish on contact with air.
Actinides: The actinides line the bottom row of the island and comprise elements 89, actinium Ac , through , lawrencium Lr. Of these elements, only thorium Th and uranium U occur naturally on Earth in substantial amounts. All are radioactive. The actinides and the lanthanides together form a group called the inner transition metals. Transition metals: Returning to the main body of the table, the remainder of Groups 3 through 12 represent the rest of the transition metals.
Hard but malleable, shiny, and possessing good conductivity, these elements are what you typically think of when you hear the word metal. Many of the greatest hits of the metal world — including gold, silver, iron and platinum — live here. Post-transition metals: Ahead of the jump into the nonmetal world, shared characteristics aren't neatly divided along vertical group lines.
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