Chemistry – 5th
January 12, 2014
1. Explain the difference between precision and accuracy. Suppose you made three different mass measurements of a sugar sample you knew to have a mass of 1.00g. How would you know whether or not the measurements were accurate? How would you know whether or not they were precise? Could the three measurements be precise, but not accurate? Explain. The difference between precision and accuracy is that precision is how close the measurements are to another, and accuracy is a measure of how close a measurement is to the true value of the measurement. If you were to make three different mass measurements of the sugar samples and you already knew that the mass was 1.00g, and you wanted to know if the other ones were accurate; you could tell by how close they are to each other and how close they are to the true value. To tell if they are precise you would have to look at the other measurements and see how close they are to each other like 2.45g and 2.40g, but they are not close to the true value so that would make them precise. Yes, the measurements could be precise but not accurate because, the other measurements could be close together but not enough to the true value to make it accurate. 2. Describe the different principles that govern the building of an electron configuration. One of the principles is the Aufbau Principle which is when electrons occupy the orbitals of the lowest energy level first. The next principle is the Pauli Exclusion Principle and this states that an orbital can hold as most two electrons. Also they must have an opposite spin and can be thought of as clockwise and counterclockwise. Another principle is the Hund’s Rule and this states that electrons occupy orbitals of the same energy level in a way that makes the amount of electrons with the same spring as large as possible. The second electrons then occupy each orbital so that the spins are paired with the first electron in the orbital.
3. Using the trends for atomic size across a period and down a group. Explain how this affects the electronegativity and ionization energy of an atom. Include in you answer the shielding effect of the electrons. Atomic size affects the electronegativity because when it goes from top to bottom it decreases value and then it increases when it moves left to right across the periodic table. For the ionization energy it increases from left to right and decreases when it moves top to bottom of the periodic table. Also, the higher the value of the ionization energy, the more challenging it is to remove the electron. If the electron has a high size, which is due to the shielding effect because it has many shields blocking the nucleus, it will have a low ionization and electronegativity. And if they electron has a low size it would have a high ionization and electronegativity. The shielding effect is owed to