ATOMIC STRUCTURE AND PROPERTIES (essential knowledge & power points)

*The periodic table shows patterns in electronic structure and trends in atomic properties. (Explain the relationship between trends in atomic properties of elements and electronic structure and periodicity.) How is the periodic table organized and how is this organization explained?

the organization of the periodic table is based on the recurring properties of the elements and explained by the pattern of electron configurations and the presence of completely or partially filled shells (and subshells) of electrons in atoms.

what does it mean if two elements are isoelectronic?

when an ion and an element have the same electron configuration

How do you write electron configurations for cations?

Cations are formed when an atom loses electrons. This is typical of metallic elements. Start with neutral atom and remove electrons from outermost s or p shell.

*Atoms and molecules can be identified by their electron distribution and energy. (Represent the electron configuration of an element or ions of an element using the Aufbau principle.) What is coulomb's law?

Coulomb's law is used to calculate the force between two charged particles. EQN:

*The mole allows different units to be compared: (Calculate quantities of a substance) What is a mole and what does it connect?

One cannot count particles directly while performing laboratory work. Thus, there must be a connection between the masses of substances reacting and the actual number of particles undergoing chemical changes.

*Chemical formulas identify substances by their unique combination of atoms. (Explain the quantitative relationship between the elemental composition by mass and the empirical formula of a pure substance.) how can the composition of pure substances be described?

Some pure substances are composed of individual molecules, while others consist of atoms or ions held together in fixed proportions as described by a formula unit.

*Atoms and molecules can be identified by their electron distribution and energy. (Represent the electron configuration of an element or ions of an element using the Aufbau principle.) What is the atom composed of?

The atom is composed of negatively charged electrons and a positively charged nucleus that is made of protons and neutrons

What is the Aufbau Principle?

The aufbau principle states that electrons enter orbitals of lowest energy first.

*Chemical formulas identify substances by their unique combination of atoms. (Explain the quantitative relationship between the elemental composition by mass and the empirical formula of a pure substance.) What is an empirical formula and how is it calculated?

The chemical formula that lists the lowest whole number ratio of atoms of the elements in a compound is the empirical formula.

*The mole allows different units to be compared: (Explain the quantitative relationship between the mass spectrum of an element and the masses of the element's isotopes.) How is the average atomic mass of an element estimated?

the average atomic mass of an element can be estimated from the weighted average of the isotopic masses using the mass of each isotope and its relative abundance.

How is Avogadro's number related to the concept of the mole?

A mole of any substance contains Avogadro's number of representative particles. A representative particle is the smallest particle of a substance that has all of the properties of that substance. 1 mole of an element = 6.022×1023 atoms 1 mole of a molecular compound or diatomic element = 6.022×1023 molecules 1 mole of an ionic compound = 6.022×1023 formula units *Molecules are composed of atoms, which are covalently bonded together. Formula units are composed of ions, which are held together by electrostatic attraction.

*Chemical formulas identify substances by their unique combination of atoms. (Explain the quantitative relationship between the elemental composition by mass and the empirical formula of a pure substance.) What is the law of definite proportions?

According to the law of definite proportions, the ratio of the masses of the constituent elements in any pure sample of that compound is always the same.

How do you write electron configurations for anions?

Anions are formed when an atom gains electrons. This is typical of nonmetallic elements. Add electrons to last unfilled subshell starting where neutral atom left off.

*The mole allows different units to be compared: (Calculate quantities of a substance) What provides a connection between the number of moles in a pure substance and the number of particles in that substance?

Avogadro's number (NA = 6.022 × 1023 mol-1) provides the connection between the number of moles in a pure sample of a substance and the number of constituent particles (or formula units) of that substance.

What might cause elements to be exceptions to the Aufbau Diagram

Because fewer electrons are sharing orbitals, electron repulsion is decreased and stability is increased.

Where are the electrons in an atom located?

Electrons are found within very specific quantized, three dimensional spaces (called orbitals) around the atom, and these spaces are defined by wave functions that are mathematical solutions to the Schrödinger wave equation. Each three-dimensional space is a probability map where one might expect to find an electron and can be thought of as a "cloud". Each of these three-dimensional spaces (orbitals) is located at a particular distance (or level/shell) from the nucleus. The levels/shells have increasing energy as one moves away from the nucleus.

*Chemical formulas identify substances by their unique combination of atoms. (Explain the quantitative relationship between the elemental composition by mass and the composition of substances in a mixture). What is elemental analysis?

Elemental analysis can be used to determine the relative numbers of atoms in a substance and to determine its purity.

*The periodic table shows patterns in electronic structure and trends in atomic properties. (Explain the relationship between trends in the reactivity of elements and periodicity.) What type of compounds to elements in the same coloumn of the periodic table tend to form?

Elements in the same column of the periodic table tend to form analogous compounds (compound having a structure similar to that of another compound, but differing from it in respect to a certain component)

*The mole allows different units to be compared: (Calculate quantities of a substance)

Expressing the mass of an individual atom or molecule in atomic mass units (amu) is useful because the average mass in amu of one particle (atom or molecule) or formula unit of a substance will always be numerically equal to the molar mass of that substance in grams. Thus, there is a quantitative connection between the mass of a substance and the number of particles that the substance contains. EQN: n = m/M

What is Ferromagnetism?

Ferromagnetism is the basic mechanism by which certain materials (such as nickel, iron and cobalt and many of their alloys) form permanent magnets. In a ferromagnetic element, electrons or atoms are grouped into domains in which each domain has the same charge. In the presence of a magnetic field, these domains line up so that charges are parallel throughout the entire substance.

What is Hund's Rule?

Hund's rule states that when electrons occupy orbitals of equal energy (degenerate orbitals), one electron occupies each orbital until all orbitals contain one electron with parallel spins.

*Atoms and molecules can be identified by their electron distribution and energy. (Represent the electron configuration of an element or ions of an element using the Aufbau principle.) What is electron configuration and how can the arrangement of electrons be described?

In atoms and ions, the electrons can be thought of as being in "shells (energy levels)" and "subshells (sublevels)", as described by the electron configuration. Inner electrons are called core electrons, and outer electrons are called valence electrons. The electron configuration is explained by quantum mechanics, as delineated in the Aufbau principle and exemplified in the periodic table of the elements.

What is molar volume?

Molar volume is the volume of 1 mole of a gas.

How can we describe the electronic structure of an atom?

The electronic structure of an atom can be described by the use of shells, sub-shells, orbitals, and spin, which, when taken together, describe the position of any given electron in an atom. Each level/shell has a number known as the principal quantum number (n). In each shell, the maximum number of electrons is given by 2(n2). Each shell is further divided into sub-shells. The number of sub-shells within any level is equal to n, and the subshells are given the letters s, p, d, and f. Each sub-shell is further divided into individual orbitals. Each orbital can hold a maximum of two electrons and that they must have opposite spin (Pauli Exclusion Principle).

*Atoms and molecules can be identified by their electron distribution and energy. (Explain the relationship between photoelectron spectrum of an atom or ion and: a. The electron configuration of the species. b. The interactions between the electrons and the nucleus.) What is photoelectron spectroscopy?

The energies of the electrons in a given shell can be measured experimentally with photoelectron spectroscopy (PES). The position of each peak in the PES spectrum is related to the energy required to remove an electron from the corresponding subshell, and the height of each peak is (ideally) proportional to the number of electrons in that subshell.

*The periodic table shows patterns in electronic structure and trends in atomic properties. (Explain the relationship between trends in the reactivity of elements and periodicity.) What determines the likelihood that two elements will form a chemical bond?

The likelihood that two elements will form a chemical bond is determined by the interactions between the valence electrons and nuclei of elements.

*The mole allows different units to be compared: (Explain the quantitative relationship between the mass spectrum of an element and the masses of the element's isotopes.) What is the significance and function of a mass spectrum?

The mass spectrum of a sample containing a single element can be used to determine the identity of the isotopes of that element and the relative abundance of each isotope in nature.

*The periodic table shows patterns in electronic structure and trends in atomic properties. (Explain the relationship between trends in atomic properties of elements and electronic structure and periodicity.) What is periodicity and what does it help to predict?

The periodicity (trends or recurring variations in element properties with the increasing atomic number) (in SAP-2.A.2) is useful to predict /estimate values of properties in the absence of data.

*Atoms and molecules can be identified by their electron distribution and energy. (Represent the electron configuration of an element or ions of an element using the Aufbau principle.) What is ionization energy and how can it be estimated?

The relative energy required to remove an electron from different subshells of an atom or ion or from the same subshell in different atoms or ions (ionization energy) can be estimated through a qualitative application of Coulomb's law. This energy is related to the distance from the nucleus and the effective (shield) charge of the nucleus.

*The periodic table shows patterns in electronic structure and trends in atomic properties. (Explain the relationship between trends in atomic properties of elements and electronic structure and periodicity.) How can periodic trends be understood?

Trends in atomic properties within the periodic table (periodicity) can be qualitatively understood through the position of the element in the periodic table, Coulomb's law, the shell model, and the concept of shielding/effective nuclear charge. These properties include: a. Ionization energy b. Atomic and ionic radii c. Electron affinity d. Electronegativity.

*The periodic table shows patterns in electronic structure and trends in atomic properties. (Explain the relationship between trends in the reactivity of elements and periodicity.) What constitutes the typical charges of atoms in ionic compounds?

Typical charges of atoms in ionic compounds are governed by their location on the periodic table and the number of valence electrons.

What do the terms paramagnetic and diamagnetic refer to?

When a species has unpaired electrons present, it is said to be paramagnetic and it will be attracted by an externally applied magnetic field. Those species with only paired electrons are not attracted by the external magnetic field and are called diamagnetic.

*Chemical formulas identify substances by their unique combination of atoms. (Explain the quantitative relationship between the elemental composition by mass and the composition of substances in a mixture). what is the difference between pure substances and mixtures and what is the significance of this?

While pure substances contain molecules or formula units of a single type, mixtures contain molecules or formula units of two or more types, whose relative proportions can vary.