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Course: High school chemistry > Unit 1
Lesson 1: Atomic structureElements and atomic number
Atoms come in a variety of types, called elements, each with a unique set of physical and chemical properties. An element is defined by the number of protons in its atoms, known as its atomic number. The periodic table organizes the elements by atomic number and provides other key information about them such as their names and chemical symbols. Created by Khan Academy.
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Why is the periodic table of elements broken into two parts?(5 votes)
Anyone who is saying there is no reason is wrong, there is always a reason for everything in science. Here are the reasons (took me half an hour to finish writing this, I hope you enjoy it :) ):
The second part of the periodic table contains 2 parts, the Lanthanide series and the Actinide series. There are 3 main reasons why scientists have taken this series out of the main body of the periodic table.
For starters, you have to understand first what electron shells and atomic orbitals are. These are ways scientist have been able to roughly predict the placement of different energy level electrons around the atomic core, in the form of orbits (If you've already taken AP Chem then skip this part). Though more precisely speaking this is just a calculated estimate of the most likely placement for the same level electrons as the form of possibility clouds by using the Schrodinger equation, an orbit is much easier to understand, so we'll go with that. There are 7 lines (excluding the two series outside the table) of the periodic table as you might have noticed, and there is a big chunk missing from the middle of the top. There are also 7 electron shells, KLMNOPQ, and 7 atomic orbitals, spdfghi. In fact, each line of the periodic table matches up with a corresponding electron shell, for example, the first line containing only Hydrogen and Helium contains elements that only have electrons in the K shell; The second line contains 8 elements, from Lithium to Neon, which all only have electrons in the K and L shell; The third line is KLM, the fourth KMLN, the fifth KLMNO and so on. As for atomic orbitals, they are sort of the shell in shell, which means that they are a new division in the electron shell, since electrons of the same shell don't all have the same energy, but they are also not distinct from each other. To categorize them, Bohr used atomic orbitals, which divides different energy electrons in the same shell into different orbitals. the nth shell contains n number of orbitals, and the orbitals with the same symbol but in different shells is differed by a number before them, which is n, the bigger the number, the higher the energy. This means that K only contains the 1s orbital, L contains 2s and 2p, M contains 3s 3p and 3d, N contains 4s 4p 4d and 4f etc.. There are always the same maximum number of electrons in orbitals with the same symbol, even if they are from different shells, s always maxes out at 2, p at 6, d at 10, f at 14 etc., each increasing by 4. Following the Lowest Energy Principle, electrons will always go into the lower energy atomic orbitals first. The energy of the same shell orbitals increase as the symbols increase, s<p<d<f<g<h<i, and the higher n is for the same symbol, the more energy the orbital contains. Now it is easy to treat the first few orbitals, you just put electrons in as the orbitals and shells increase, 2 for 1s, 2 for 2s, 6 for 2p, 2 for 3s, 6 for 3p. But as we reach the last orbital of the M shell, things change. We now face the choice of putting the electron into 4s or 3d. You might think that 4s being in the N shell it will have higher energy, but the fact is, 3d is the d orbital, which itself contains more energy than the s orbital. The fact is from here on we apply the Aufbau principle, which basically tells AP Chem students to memorize the following: after 3p it is: 4s - 3d - 4p - 5s - 4d - 5p - 6s - 4f - 5d - 6p... Here is a link for a detailed description of the Aufbau principle visually from wikipedia: https://en.wikipedia.org/wiki/Aufbau_principle#/media/File:Aufbau_Principle-en.svg
So now it might be dawning on you, as the lines of the periodic table increase, we are getting more and more atoms since the number of electrons in each shell increases, thus we have more atoms to deal with. This is why there is a big chunk missing, cuz the upper few lines only have that many elements. But there is the opposite problem for the 6th and 7th line: They contain more than 18 elements. This is the First reason why the Actinide and Lanthanide series are written separately from the main body part, to make the whole table look much clearer than if they wrote everything out as one.
The second reason has to do with the valence electron shell. The valence electron shell is the part of the electron shell that is responsible for giving the atom its most common ionic charge, or more simply speaking, it is the most outer electron shell of the atom. According to which atomic orbital these electrons are in, chemists assigned names to different parts of the periodic table, with each part containing elements of the same valence orbital type. The IA group to the IIA group are known as the s block, with ns as the valence orbitals; the IIIB group to the VIII group are known as the d block, with (n-1)d^(1-9)ns as the valence orbitals; the IB group to the IIB group are known as the ds block, with (n-1)d^(10)ns as the valence orbitals; the IIIA group to the 0th group are known as the p block, with nsnd^(1-6) as the valence orbitals, the only exception being Helium, which has no p orbitals. Now the Actinide and Lanthanide series are in and are the only elements in the f block, which means their valence orbitals are (n-2)f(n-1)dns. This is the reason why chemists decided to isolate this particular set of elements, and not any other set.
The third reason is because the elements in the Lanthanide and Actinide series have special characteristics that no other set of or lone element(s) have. (Note that these elements have similar characteristics as well, and that in mines of any of these elements, all or many of the elements of the same series stick to each other in the mine, making it hard to separate them.) For example, the Lanthanide series has a famous characteristic called the Lanthanide contraction phenomenon. It states that although the elements in the series like any of the other periods have decreasing atomic radii as the atomic number increases, the rate of decrease in the Lanthanide series is much slower than any other periods. It is the same thing with the Actinide series, the phenomenon is known as Actinide contraction. Other patterns in both include the three plus cations in the series' ionic color change in a pattern of "colorless -> colored -> colorless", and that most of the elements in both series tend to be a good source of electromagnetic material.
Alright, I'm done, I hope this helps :D(15 votes)
so If I have a potassium (K) and add a proton, it is no longer a potassium, it's a calcium (Ca) right?(6 votes)
Yes, if you add a proton to potassium you get calcium.(7 votes)
How did each element get their name? Like who came up with the names?(4 votes)
Currently the International Union of Pure and Applied Chemistry (IUPAC) decides elements' names. A lot of elements are named after famous scientists, places, planets, or mythological figures. Other times, their names are associated with their properties or even other elements. Hope this helps! :)(6 votes)
How come protons neutrons and electrons aren't the smallest particles on earth, since they're INSIDE the atom?(3 votes)
They aren't the smallest because they are made of quarks, which are the new smallest thing since atoms(6 votes)
- How did each element get their name? Like who came up with the names?(2 votes)
- The names of the elements are usually given by the people who discovered them. Or the places where they were found. Others have names based on mythology, and still others for their appearance.(6 votes)
- is gold and crystals are made of current atoms?(3 votes)
- Yup, gold is an element and crystals are made of various elements depending on what kind of crystal it is.(4 votes)
Wait so if I'm getting this right, elements are atoms? So they're basically different names for the same things? Or are they different?(3 votes)
An element is a pure substance made entirely of one type of atom.(3 votes)
- Why is the periodic table of elements broken into two parts?(2 votes)
For practicality. The lanthanides (the top row of the bottom block) usually fits between barium (56) and hafnium (72). The actinides are normally right below the lanthanides, between radium (88) and rutherfordium (104). These two groups are separated from the main body to save space, because the normal way make the table extremely long (14 extra boxes wide).(5 votes)
What is Og and when was it discovered?(2 votes)
According to google Og = Oganesson and it was discovered in 2002. It wasn't named Oganesson at he time it used to be called Ununoctium.(4 votes)
Why is the periodic table organized how it is? Why is there a large gap at the top?(3 votes)
(Simplifcation)
It has to do with the capacity of each electron shell.
The row of an element on the periodic table is known as the 'period'. The period tells us the number of electron shells that are occupied.
The column of an element on the periodic table is known as the 'group'. The group tells us the number of valence electrons (electrons on the outermost shell).
Going up the elements, protons increase by1and electrons also increase by1.
- Shell1can only hold a maximum of2electrons.
- Shell2can hold up to8electrons.
- The third shell can hold8electrons initially. In period4, shell4gains2electrons before further filling shell3to up to18electrons in the period4transition metals.
So most transition metals have2valence electrons.
The gaps on period2and3are formed this way to accommodate for the transition metals.
The even larger hydrogen-helium gap though? The rightmost group is reserved for the noble gases - elements with a completely filled valence shell. Helium has2electrons, completely filling shell1.
I hope this helps?(3 votes)
Video transcript
- [Instructor] We know that
everything in the universe is composed of atoms, but not all atoms are the same. There are many different types
of atoms called elements, each with a unique set of
physical and chemical properties. Many elements are
probably familiar to you. Oxygen and carbon, for
example, are elements, and so is gold. Others may be less familiar such as bismuth, xenon, and osmium. A particular element is identified by the number of protons in its atoms. And the number of protons
in the nucleus of an atom is its atomic number,
represented by the symbol Z. For example, helium has
an atomic number of two. That means that every
helium atom has two protons. And here's another example, iron, its atomic number is 26, so every iron atom has 26 protons. An element's atomic
number can also tell us the number of electrons in a
neutral atom of an element. Remember, equal and opposite
charges cancel each other out so to be neutral, an atom must have an
equal number of protons, which have a charge of 1+, and electrons, which have a charge of 1-. This means that our helium
atom must have two electrons and our iron atom must have 26 electrons. All of the known elements are organized according
to their atomic numbers in the periodic table. The periodic table lists the elements in order of increasing atomic number as you go from left to right
and from top to bottom. The elements are further
organized into columns based on their properties. Elements in the same column tend to have similar physical
and chemical properties. Every element is represented
by a chemical symbol, a unique one or two letter abbreviation that appears below the
element's atomic number on the periodic table. Many chemical symbols are based on the English
name for an element. For example, the symbol for hydrogen is H, and the symbol for aluminum is Al. But some chemical symbols are based on the Latin
name for the element. For example, the symbol for lead is Pb, which actually comes from
its Latin name plumbum. Notice that whenever the chemical symbol for an element has two letters, the second letter is written in lowercase. All of this information is contained inside of each element's
box on the periodic table. For example, here's the box
for the element nitrogen. At the top of the box is nitrogen's atomic
number, which is seven. Remember that this is equal to the number of protons
in each atom of nitrogen as well as the number of electrons. Below that is nitrogen's
chemical symbol, N, followed by its name. Often, you'll also see another number listed at the bottom of an elements box, which has to do with atomic mass. We'll cover details about
this and another video. What's neat about having all of this information in one place is that if we know one
detail about an element, either it's atomic number,
chemical symbol, or a name, we can often use the periodic table to find out the other details. Let's take a look at a few examples. Say we have the element phosphorus, what is its atomic number
and chemical symbol? Looking through the periodic table, we can find phosphorus and see that its atomic number is 15 and its chemical symbol is P. Let's do another example. Say we know the chemical symbol Hg, what is this element's name and how many protons does it have? Here is the symbol Hg
on the periodic table. Its name is mercury, and its atomic number is 80 so it has 80 protons. Let's reveal. The universe is made up of different types of
atoms called elements, and these elements are
organized by atomic number in the periodic table. So, the next time that you
stare up at the starry sky, you know that everything out
there is made up of elements.