What Particles Make Up the Atom and How They Interact
An atom is made of protons, neutrons, and electrons. Protons have a positive electric charge, neutrons have no charge, and electrons have a negative charge. Protons and neutrons form the nucleus. Electrons occupy the region around it.
The number of protons identifies the element. The number of neutrons can vary between atoms of the same element, and the number of electrons can change when an atom becomes an ion.
The three particles
| Particle | Charge | Location | Main role |
|---|---|---|---|
| Proton | +1 | Nucleus | Determines the element |
| Neutron | 0 | Nucleus | Adds to the atom’s mass and affects nuclear stability |
| Electron | −1 | Around the nucleus | Influences chemical behavior and bonding |
Protons and neutrons are called nucleons because they make up the nucleus. Their masses are similar, and each is much heavier than an electron. As a result, nearly all of an atom’s mass is concentrated in its nucleus Encyclopaedia Britannica.
The nucleus is very small compared with the full size of an atom. Electrons occupy the surrounding region, often described as an electron cloud. In quantum physics, this cloud describes where an electron is likely to be found, not a set of tracks around the nucleus.
In a neutral atom, the number of electrons equals the number of protons, so their charges balance. If an atom gains or loses electrons, it becomes an ion with a net charge. Its proton count stays the same, so it remains the same element.
What determines an element?
An element is defined by its number of protons, also called its atomic number. Every carbon atom has six protons; every oxygen atom has eight. Changing the number of protons changes the element NIST.
Neutrons affect an atom’s mass and the stability of its nucleus, but they do not determine its element. Atoms of the same element with different numbers of neutrons are called isotopes. The mass number is the total number of protons and neutrons in the nucleus.
Electrons influence how atoms interact and form bonds. Changing an atom’s electrons can change its charge and chemical behavior, while changing its protons changes the element itself.
How the particles stay together
The electromagnetic force attracts particles with opposite charges and repels particles with the same charge. In an atom, the positively charged nucleus attracts negatively charged electrons.
Inside the nucleus, protons repel one another because they have the same positive charge. The strong nuclear force binds nucleons together at very short distances. Neutrons contribute to this binding without adding electric charge.
Electromagnetic attraction links the nucleus and electrons, while the strong force binds the nucleus. Chemical reactions involve changes in how electrons are arranged or shared. Nuclear reactions involve changes in the nucleus.
One example: sodium and chlorine
A neutral sodium atom has 11 protons and 11 electrons. A neutral chlorine atom has 17 protons and 17 electrons. When they form sodium chloride, an electron transfers from sodium to chlorine.
Sodium then has a positive charge, and chlorine has a negative charge. Their opposite charges attract, forming an ionic bond. The nuclei do not change during this electron transfer.
Key Takeaways
- Protons and neutrons form the nucleus; electrons occupy the region around it.
- An element’s identity depends on its proton count.
- Isotopes have different numbers of neutrons. Ions have gained or lost electrons.
- Electromagnetic attraction binds electrons to the nucleus, while the strong nuclear force binds nucleons together.
- Chemical bonding changes how electrons are arranged or shared, not an atom’s proton count.
