No problem. We'll do well to cover it in a future lesson.

write a concise note on d following concept; 
photochemical reactions
mechanism of photochemical reactions in simple inorganic compound.,.... please I knw is out of our syllabus but I need hlp on this... thanks

<h2>Summary of lessons so far</h2>
<h3>The Periodic Table</h3>
<p>The discovery of the periodic recurrence of similar properties among the <a data-lesson="elements" data-subject="chemistry" data-tutorial="classification-of-matter" href="https://app.ulearngo.com/chemistry/classification-of-matter/elements">elements</a> led to the formulation of the periodic table, in which the elements are arranged in order of increasing <a data-lesson="atomic-and-atomic-mass-number" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/atomic-and-atomic-mass-number">atomic number</a> in rows known as periods and columns known as groups.</p>
<p>Elements in the same group of the periodic table have similar chemical properties. Elements can be classified as metals, metalloids, and nonmetals, or as a main-group elements, transition metals, and inner transition metals. Groups are numbered 1–18 from left to right. The elements in group 1 are known as the alkali metals; those in group 2 are the alkaline earth metals; those in 15 are the pnictogens; those in 16 are the chalcogens; those in 17 are the halogens; and those in 18 are the noble gases.</p>
<h3>Molecular and Ionic Compounds</h3>
<p id="fs-idp122679888">Metals (particularly those in groups 1 and 2) tend to lose the number of electrons that would leave them with the same number of electrons as in the preceding noble gas in the periodic table. By this means, a positively charged ion is formed. Similarly, nonmetals (especially those in groups 16 and 17, and, to a lesser extent, those in Group 15) can gain the number of electrons needed to provide atoms with the same number of electrons as in the next noble gas in the periodic table. Thus, nonmetals tend to form negative ions. Positively charged ions are called cations, and negatively charged ions are called anions. Ions can be either monatomic (containing only one atom) or polyatomic (containing more than one atom).</p>
<p id="fs-idp57422256">Compounds that contain ions are called ionic compounds. Ionic <a data-lesson="compounds-2" data-subject="chemistry" data-tutorial="quantitative-aspects-chemical-change" href="https://app.ulearngo.com/chemistry/quantitative-aspects-chemical-change/compounds-2">compounds</a> generally form from metals and nonmetals. Compounds that do not contain ions, but instead consist of atoms bonded tightly together in molecules (uncharged groups of atoms that behave as a single unit), are called covalent compounds. Covalent compounds usually form from two nonmetals.</p>
<h3>Chemical Nomenclature</h3>
<p>Chemists use nomenclature rules to clearly name compounds. Ionic and <a data-lesson="molecular-compounds" data-subject="chemistry" data-tutorial="atoms-molecules-ions" href="https://app.ulearngo.com/chemistry/atoms-molecules-ions/molecular-compounds">molecular compounds</a> are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to –<em data-effect="italics">ide</em>. For example, K<sub>2</sub>O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge. Thus, FeCl<sub>2</sub> is iron(II) chloride and FeCl<sub>3</sub> is iron(III) chloride. Some compounds contain polyatomic ions; the names of common polyatomic ions should be memorized.</p>
<p>Molecular compounds can form compounds with different ratios of their elements, so prefixes are used to specify the numbers of atoms of each element in a molecule of the compound. Examples include SF<sub>6</sub>, <a data-lesson="sulfur" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/sulfur">sulfur</a> hexafluoride, and N<sub>2</sub>O<sub>4</sub>, dinitrogen tetroxide.</p>
<p>Acids are an important class of compounds containing <a data-lesson="hydrogen-reactions" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/hydrogen-reactions">hydrogen</a> and having special nomenclature rules. Binary acids are named using the prefix <em data-effect="italics">hydro-</em>, changing the –<em data-effect="italics">ide</em> suffix to –<em data-effect="italics">ic</em>, and adding “acid;” HCl is hydrochloric acid. Oxyacids are named by changing the ending of the anion (–<em data-effect="italics">ate</em> to –<em data-effect="italics">ic</em> and –<em data-effect="italics">ite</em> to –<em data-effect="italics">ous</em>), and adding “acid;” H<sub>2</sub>CO<sub>3</sub> is carbonic acid.</p>
<h2>Glossary of Words</h2>
<h3>Actinide</h3>
<p>inner transition metal in the bottom of the bottom two rows of the periodic table</p>
<h3>Alkali metal</h3>
<p>element in group 1</p>
<h3>Alkaline earth metal</h3>
<p>element in group 2</p>
<h3>Binary acid</h3>
<p>compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)</p>
<h3>Binary compound</h3>
<p>compound containing two different elements.</p>
<h3>Chalcogen</h3>
<p>element in group 16</p>
<h3>Covalent bond</h3>
<p>attractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms</p>
<h3>Covalent compound</h3>
<p>(also, molecular compound) composed of molecules formed by atoms of two or more different elements</p>
<h3>Group</h3>
<p>vertical <a data-lesson="obtaining-nitrogen" data-subject="chemistry" data-tutorial="chemistry-real-world" href="https://app.ulearngo.com/chemistry/chemistry-real-world/obtaining-nitrogen">column</a> of the periodic table</p>
<h3>Halogen</h3>
<p>element in group 17</p>
<h3>Inert gas</h3>
<p>(also, noble gas) element in group 18</p>
<h3>Inner transition metal</h3>
<p>(also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide</p>
<h3>Ionic bond</h3>
<p>electrostatic <a data-lesson="physical-properties-and-intermolecular-forces" data-subject="chemistry" data-tutorial="organic-molecules" href="https://app.ulearngo.com/chemistry/organic-molecules/physical-properties-and-intermolecular-forces">forces</a> of attraction between the oppositely charged ions of an ionic compound</p>
<h3>Ionic compound</h3>
<p>compound composed of cations and anions combined in ratios, yielding an electrically neutral substance</p>
<h3>Lanthanide</h3>
<p>inner transition metal in the top of the bottom two rows of the periodic table</p>
<h3>Main-group element</h3>
<p>(also, representative element) element in columns 1, 2, and 12–18</p>
<h3>Metal</h3>
<p>element that is shiny, malleable, good conductor of <a data-lesson="calorimetry" data-subject="chemistry" data-tutorial="thermochemistry" href="https://app.ulearngo.com/chemistry/thermochemistry/calorimetry">heat</a> and electricity</p>
<h3>Metalloid</h3>
<p>element that conducts heat and electricity moderately well, and possesses some <a data-lesson="properties-of-metals" data-subject="chemistry" data-tutorial="bonding-atomic-combinations" href="https://app.ulearngo.com/chemistry/bonding-atomic-combinations/properties-of-metals">properties of metals</a> and some properties of nonmetals</p>
<h3>Molecular compound</h3>
<p>(also, covalent compound) composed of molecules formed by atoms of two or more different elements</p>
<h3>Monatomic ion</h3>
<p>ion composed of a single atom</p>
<h3>Noble gas</h3>
<p>(also, inert gas) element in group 18</p>
<h3>Nomenclature</h3>
<p>system of rules for naming objects of interest</p>
<h3>Nonmetal</h3>
<p>element that appears dull, poor conductor of heat and electricity</p>
<h3>Oxyacid</h3>
<p>compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)</p>
<h3>Oxyanion</h3>
<p>polyatomic anion composed of a central atom bonded to <a data-lesson="occurrence-preparation-and-compounds-of-oxygen" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/occurrence-preparation-and-compounds-of-oxygen">oxygen</a> atoms</p>
<h3>Period</h3>
<p>(also, series) horizontal row of the periodic table</p>
<h3>Periodic law</h3>
<p>properties of the elements are periodic function of their atomic numbers.</p>
<h3>Periodic table</h3>
<p>table of the elements that places elements with similar chemical properties close together</p>
<h3>Pnictogen</h3>
<p>element in group 15</p>
<h3>Polyatomic ion</h3>
<p>ion composed of more than one atom</p>
<h3>Representative element</h3>
<p>(also, main-group element) element in columns 1, 2, and 12–18</p>
<h3>Series</h3>
<p>(also, period) horizontal row of the period table</p>
<h3>Transition metal</h3>
<p>element in columns 3–11</p>

Chemistry generally explores the substances of which matter is composed, the investigation of their properties and reactions, and the use of such reactions to form new substances. 

Chemistry

Summarizing the Periodic Table, Compounds and Nomenclature

Discover the composition of matter, early ideas in atomic theory, atomic structure and symbolism, the periodic table, and chemical nomenclature in this tutorial on atoms, molecules, and ions.


Summarizing the Periodic Table, Compounds and Nomenclature

Track Your Learning Progress

Earlier discussion