2.4
Electron Behavior
Electrons are negatively charged subatomic particles that are attracted to an orbit around the positively-charged nucleus of an atom. They reside in l…
Electrons are small subatomic particles with a negative electrical charge.
Because they are negatively charged, electrons are attracted to the positively charged nucleus. They occupy energy levels, called shells, around the nucleus. Each energy level contains smaller regions called orbitals, where electrons are most likely to be found.
Electrons closest to the nucleus occupy the first energy level, which has the lowest energy. This level contains only one orbital, and each orbital can hold up to two electrons. That’s why the first energy level can hold up to two electrons.
Additional electrons fill higher energy levels, which contain more orbitals and can hold more electrons.
Electrons in the outermost energy level are called valence electrons.
Valence electrons shape the properties of an element because they can be transferred or shared with other atoms. This transfer or sharing allows atoms to form ionic or covalent chemical bonds.
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Q1: What are electrons and why are they attracted to the nucleus?
Electrons are negatively charged subatomic particles that orbit the nucleus of an atom. Because the nucleus is positively charged, it attracts electrons through opposite electrical charges. This attraction keeps electrons in orbit around the nucleus at specific energy levels called shells.
Q2: How are electrons organized in energy levels and orbitals?
Electrons occupy energy levels, or shells, around the nucleus, with each shell containing smaller regions called orbitals where electrons are most likely found. The first energy level has one orbital holding up to two electrons. Higher energy levels contain more orbitals and can hold more electrons, with electrons farther from the nucleus carrying more energy.
Q3: What are valence electrons and why do they matter?
Valence electrons are electrons in the outermost energy level of an atom. They shape an element's chemical properties because they can be transferred or shared with other atoms, allowing atoms to form ionic or covalent bonds and participate in chemical reactions.
Q4: How did J. J. Thomson discover the electron?
Thomson used cathode ray tubes in the late 1890s, directing beams between charged metal plates. He observed the beam deflected toward the positive plate, indicating the particles were negatively charged. Calculating the mass-to-charge ratio revealed these particles were tiny, about 1/2000 the mass of any known atom, leading to the electron's discovery.
Q5: Why do electrons closer to the nucleus have lower energy than those farther away?
Electrons closest to the nucleus experience stronger attraction to the positive charge and occupy the lowest energy level. As distance from the nucleus increases, the attraction weakens and electrons carry more energy. The outer shells have more space available, allowing them to hold more electrons at higher energy levels.
Q6: How does the number of electrons relate to atomic mass and charge?
Thomson's experiments revealed that atoms contain many electrons, each with tiny mass. The discovery of protons and neutrons later explained how atoms maintain overall neutral charge despite containing numerous negatively charged electrons. These subatomic particles account for an atom's mass and electrical neutrality.
Q7: What determines how many electrons each energy level can hold?
The number of orbitals in each energy level determines electron capacity. The first energy level contains one orbital holding up to two electrons. Higher energy levels contain progressively more orbitals, allowing outer shells to accommodate more electrons than inner shells, creating the characteristic electron distribution in atoms.