Which atom has the electron configuration \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{10} 4 p^{6} 5 s^{2} 4 d^{2} ?\)

The atomic number is a fundamental property of an element that reveals a lot about its characteristics. It is denoted as 'Z' and represents the number of protons found in the nucleus of an atom. Since atoms are electrically neutral, the atomic number also tells us the number of electrons in a neutral atom.

For example, in our exercise, the goal was to determine which element has a certain electron configuration. The atomic number is key in this determination because it's equivalent to the total number of electrons in the atom when it is not an ion. By matching the counted electrons to the atomic number in the periodic table, students can identify the element in question.

Importance in Chemical Properties

Chemical properties are greatly influenced by the atomic number, as elements with the same number of valence electrons often show similar chemical behavior. That's why elements are arranged in groups on the periodic table based on their atomic number, highlighting trends in reactivity and other chemical properties.

The periodic table is a systematic way of organizing elements based on their chemical properties, and the atomic number plays a crucial role in this organization. Elements are arranged in order of increasing atomic number from left to right and top to bottom.

The table is divided into rows called periods and columns known as groups or families. Each period corresponds to the filling of a different electron shell, which is why elements in the same period have the same number of atomic orbitals. For instance, the electron configuration in the exercise leads to a 'Z' of 40, placing the element in the 5th period, since the highest principle quantum number 'n' is 5 for the 5s orbital.

Discovering Element Trends

Studying the periodic table allows students to predict and understand trends in element properties, such as ionization energy, electronegativity, and atomic size. Each group of elements tends to display similar behaviors and properties, aiding in predicting how an element might react in a chemical reaction.

Electron counting is critical in determining the electron configuration of an atom or a molecule, which in turn can reveal much about its reactivity and chemical bonding. The electron configuration refers to the distribution of electrons among the different orbitals around the nucleus. One straightforward method to determine the electron configuration is by counting the number of electrons using the superscripts in the notation, as illustrated in the exercise.In identifying elements or ions, summing the electron counts from each orbital gives the total number of electrons, which will match an element's atomic number on the periodic table. A correct electron count is vital in ensuring the element is identified accurately.

Writing Electron Configurations

To write out electron configurations, recall that each orbital can hold a set number of electrons: s can hold 2, p can hold 6, d can hold 10, and f can hold 14. Follow the order of ascending energy levels, often remembered by the 'Aufbau principle', which is a useful guide for filling the orbitals in the correct sequence. This knowledge is not just essential for solving problems from textbooks; it lays the groundwork for understanding chemical reactions, the nature of light and color, magnetism, and even the structure of molecules.