All atoms have the same number of electrons as protons, so the positive and negative charges "cancel out", making atoms electrically neutral. Unlike protons and neutrons, which are located inside the nucleus at the center of the atom, electrons are found outside the nucleus. Because opposite electric charges attract one another, negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus.
The figure below is a common way to represent the structure of an atom. It shows the electron as a particle orbiting the nucleus, similar to the way that planets orbit the sun. However, this is an incorrect perspective, as quantum mechanics demonstrates that electrons are more complicated.
A proton is one of three main particles that make up the atom. Protons are found in the nucleus of the atom. This is a tiny, dense region at the center of the atom. Together with neutrons, they make up virtually all of the mass of an atom. Atoms of all elements—except for most atoms of hydrogen—have neutrons in their nucleus.
Unlike protons and electrons, which are electrically charged, neutrons have no charge—they are electrically neutral. The zero stands for "zero charge". As you might have already guessed from its name, the neutron is neutral. In other words, it has no charge whatsoever and is therefore neither attracted to nor repelled from other objects. Neutrons are in every atom with one exception , and they are bound together with other neutrons and protons in the atomic nucleus.
Before we move on, we must discuss how the different types of subatomic particles interact with each other. When it comes to neutrons, the answer is obvious. Since neutrons are neither attracted to nor repelled from objects, they don't really interact with protons or electrons beyond being bound into the nucleus with the protons. It is called the 1s orbital because it is spherical around the nucleus.
The 1s orbital is always filled before any other orbital. Hydrogen has one electron; therefore, it has only one spot within the 1s orbital occupied. This is designated as 1s 1 , where the superscripted 1 refers to the one electron within the 1s orbital.
Helium has two electrons; therefore, it can completely fill the 1s orbital with its two electrons. This is designated as 1s 2 , referring to the two electrons of helium in the 1s orbital.
On the periodic table, hydrogen and helium are the only two elements in the first row period ; this is because they are the sole elements to have electrons only in their first shell, the 1s orbital.
The second electron shell may contain eight electrons. After the 1s orbital is filled, the second electron shell is filled, first filling its 2s orbital and then its three p orbitals. When filling the p orbitals, each takes a single electron; once each p orbital has an electron, a second may be added.
Lithium Li contains three electrons that occupy the first and second shells. Two electrons fill the 1s orbital, and the third electron then fills the 2s orbital. Its electron configuration is 1s 2 2s 1. Neon Ne , on the other hand, has a total of ten electrons: two are in its innermost 1s orbital, and eight fill its second shell two each in the 2s and three p orbitals.
Electrons are one of three main types of particles that make up atoms. The other two types are protons and neutrons. Unlike protons and neutrons, which consist of smaller, simpler particles, electrons are fundamental particles that do not consist of smaller particles. They are a type of fundamental particles called leptons.
All leptons have an electric charge of -1 or 0. For an excellent video about electrons and other fundamental particles in atoms, go to this URL:. Electrons are extremely small. Unlike protons and neutrons , which are located inside the nucleus at the center of the atom, electrons are found outside the nucleus.
Because opposite electric charges attract each other, negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus. The Figure below is a common way to represent the structure of an atom.
It shows the electron as a particle orbiting the nucleus, similar to the way that planets orbit the sun. The region where an electron is most likely to be is called an orbital. Each orbital can have at most two electrons. Some orbitals , called S orbitals, are shaped like spheres, with the nucleus in the center. An S orbital is pictured in Figure below.
Where the dots are denser, the chance of finding an electron is greater. Also pictured in Figure below is a P orbital. P orbitals are shaped like dumbbells, with the nucleus in the pinched part of the dumbbell. You can see animated, three-dimensional models of orbitals at the following URL. Q: How many electrons can there be in each type of orbital shown in the Figure above? A: There can be a maximum of two electrons in any orbital, regardless of its shape.
A: The nucleus is at the center of each orbital. It is in the middle of the sphere in the S orbital and in the pinched part of the P orbital. Electrons are located at fixed distances from the nucleus, called energy levels. You can see the first three energy levels in the Figure below. The diagram also shows the maximum possible number of electrons at each energy level.
At the lowest energy level , which has the least energy, there is just one orbital, so this energy level has a maximum of two electrons. Electrons at higher energy levels, which are farther from the nucleus, have more energy.
They also have more orbitals and greater possible numbers of electrons. They determine many of the properties of an element. Atoms may share or transfer valence electrons. Shared electrons bind atoms together to form chemical compounds.
You can see all of these ideas in action at the following URL scroll down to the animation at the bottom of the Web page. Q: If an atom has 12 electrons, how will they be distributed in energy levels? A: The atom will have two electrons at the first energy level, eight at the second energy level, and the remaining two at the third energy level.
Q: Sometimes, an electron jumps from one energy level to another. How do you think this happens? A: To change energy levels, an electron must either gain or lose energy. They are extremely small and have an electric charge of All atoms have the same number of electrons as protons. This force of attraction keeps electrons constantly moving around the nucleus. The region where an electron is most likely to be found is called an orbital. Electrons at lower energy levels have less energy than electrons at higher energy levels.
Research the discovery of electrons at the following URLs, and then answer the questions below. Who discovered electrons? When were they discovered? What was the significance of the discovery of electrons? Where did Thomson think electrons were located in the atom? How does this differ from the modern view of electrons presented above? Sketch a model of a beryllium atom, which has four protons, five neutrons , and four electrons.
Your model should include the placement of electrons at the appropriate energy levels. What are valence electrons? Why are they so important?
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