So just keep in mind we have these two forces at work within any given Adam. This electron and blue is experiencing pushing away because the electron that's highlighted is repelling it further and further away from the nucleus. So Valence electrons are gonna be pushed further away from the nucleus here. Because positive charge binds electrons more strongly, the second ionization energy of an element is always higher than the first. We're going to say as that increases, that's going to cause an increase in the repulsive force. An elements second ionization energy is the energy required to remove the outermost, or least bound, electron from a 1+ ion of the element. Now our shielding constant is the measurement is the measurement of the repulsive force between our valence electrons or outer shell electrons and the inner core electrons here. At the same time, we have our shielding constant. Thus, as we move across a period, the nuclear charge increases while the number of electron shells remains constant, causing the atomic radius to decrease. So the electrons are gonna be pulled closer to the nucleus. And if you're attracted to one another, you're gonna come closer together. We're going to say here that the greater the effective nuclear charge than the greater the attractive force between the nucleus and the electron. So here, the attractive force between that electrons and the nucleus can be explained by the effective nuclear charge. But repulsion from one another now effective nuclear charge abbreviated as Z E f is the measurement of attractive force between protons and electrons. So these electrons are experiencing these two different forces at the same time, attraction for the nucleus. Well, the electron here is negatively charged, so it would form an attraction to the nucleus here, which is positively charged at the same time, this outer electron here, since it's also negative, would repel this highlighted electron. It can be approximated by the equation: Zeff Z S, where Z is the atomic number and S is the number of shielding electrons. So, yes, the atomic number of an element is directly proportional to the effective nuclear charge, if you look at it from this point of view. For example, the atomic number of lithium is 3, and also the number of protons in the nucleus of lithium is 3. B) Core electrons screen the nuclear charge more effectively than valence electrons. So let's say that we're examining this electron here. Basically, the atomic number is the same as the number of protons in the nucleus. Periodic trends are patterns in elements on the periodic table. This video introduces the effective nuclear charge of an element/ion and how you can use it to predict trends on the periodic table like atomic radius, elect. A) The effective nuclear charge is the force exerted by the nucleus onto an electron. Now within an atom and electron experiences two different forces it experiences and attraction by the nucleus and a repulsion by surrounding electrons.
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