D And F Block Elements Class 12 Notes Pdf Download ((EXCLUSIVE))

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The elements of Group 1 and Group 2 of the modern periodic table are called S-block elements. Two types of s block elements are possible, i.e., the elements with one electron (s1) or the elements with two electrons (s2) in their s-subshell.

D And F Block Elements Class 12 Notes Pdf Download

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S-block elements having only one electron in their s-orbital are called group one or alkali metals, whereas the s block elements having two electrons filling their s-orbital are called group two or alkaline earth metals.

The electrons present in an atom occupy various sub-orbitals of available energy levels in the order of increasing energy. The last electron of an atom may find itself in either of the s, p, d and f subshells. Accordingly, the elements of the atom having their last valence electron present in the s-suborbital are called s block elements.

Both alkali and alkaline earth elements show a regular gradation in their properties among their respective group elements. But the first member of both S block elements, namely, Lithium and Beryllium, differ much from the rest of their members, but at the same time, they resemble more with the diagonal element present in the next column.

It is observed that the physical and chemical properties of these s block elements change in a particular trend as the atomic number of the elements increases. Changes in the various properties of the group are as mentioned below:

When the s block elements of the modern periodic table are observed, it is seen that the size of the alkali metals is larger compared to other elements in a particular period. As the atomic number increases, the total number of electrons increases along with the addition of shells.

A diagonal relationship in s block elements exists between adjacent elements, which are located in the second and third periods of the periodic table. For example, the lithium of group 1A and the second period shows similarities with the properties of magnesium, which are located in the 2nd group and 3rd period.

The properties of s block elements vary significantly when compared to the other elements of the sub-group they belong to. The diagonal neighbours show a lot of similarities. Such a relationship is exhibited as you move left to the right and down the group; the periodic table has opposing factors.

For example, the electronegativity of the s block elements increases as we go across the period and decreases as we go down the group. Therefore, when it is moved diagonally, the opposite tendencies cancel out, and the value of electronegativity almost remains the same.

S-block elements are strong electropositive elements with low reduction potential, indicating their strong reducing ability compared to others. So, substances having lower reducing ability than them will not be able to reduce them. Reducing the ability of an atom is related to the ease of releasing electrons for reduction. Decreasing ionization energy down the column suggests that caesium is a stronger reducing agent than Lithium.

S block elements, or their halides on exposure to flame, undergo electronic transitions in the visible region of the light spectrum. Hence, they induce characteristic colour into the flame. The colours are as follows:

A simple selector is eithera type selector or universal selector followed immediatelyby zero or more attributeselectors, ID selectors, or pseudo-classes, in any order. The simpleselector matches if all of its components match.Note: the terminology used here in CSS 2.1 isdifferent from what is used in CSS3. For example, a "simple selector"refers to a smaller part of a selector in CSS3 than in CSS 2.1.See the CSS3 Selectors module [CSS3SEL].A selector is a chain of one or moresimple selectors separated by combinators. Combinators are: white space,">", and "+". White space may appear between a combinator and thesimple selectors around it.The elements of the document tree that match a selector are calledsubjects of the selector.A selector consisting of a single simple selector matches any elementsatisfying its requirements. Prepending a simple selector andcombinator to a chain imposes additional matching constraints, so thesubjects of a selector are always a subset of the elements matchingthe last simple selector.One pseudo-element may be appendedto the last simple selector in a chain, in which case the styleinformation applies to a subpart of each subject.5.2.1 GroupingWhen several selectors share the same declarations, they may begrouped into a comma-separated list.

Here, because the selector EXAMPLE[notation=octal] ismore specific than the typeselector alone, the style declarations in the second rule will overridethose in the first for elements that have a "notation" attribute valueof "octal". Care has to be taken that all property declarations thatare to apply only to the default case are overridden in the non-defaultcases' style rules.5.8.3 Class selectors Working with HTML, authors may use the period (.)notation as an alternative to the ~= notation whenrepresenting the class attribute. Thus, for HTML,div.value and div[class~=value] have thesame meaning. The attribute value must immediately follow the"period" (.). UAs may apply selectors using theperiod (.) notation in XML documents if the UA has namespace specificknowledge that allows it to determine which attribute is the"class" attribute for the respective namespace. One suchexample of namespace specific knowledge is the prose in thespecification for a particular namespace (e.g., SVG 1.1 [SVG11]describes the SVG"class" attribute and how a UA should interpret it, andsimilarly MathML 3.0 [MATH30] describes the MathML"class" attribute.)Example(s):

This rule matches when class="pastoral blue aquamarine" but does not match for class="pastoralblue". Note. CSS gives so muchpower to the "class" attribute, that authors could conceivably designtheir own "document language" based on elements with almost noassociated presentation (such as DIV and SPAN in HTML) and assigningstyle information through the "class" attribute. Authors should avoidthis practice since the structural elements of a document languageoften have recognized and accepted meanings and author-defined classes maynot.Note: If an element hasmultiple class attributes, their values must be concatenated withspaces between the values before searching for the class. As of thistime the working group is not aware of any manner in which thissituation can be reached, however, so this behavior is explicitlynon-normative in this specification.5.9 ID selectorsDocument languages may contain attributes that are declared to beof type ID. What makes attributes of type ID special is that no twosuch attributes can have the same value; whatever the documentlanguage, an ID attribute can be used to uniquely identify itselement. In HTML all ID attributes are named "id"; XMLapplications may name ID attributes differently, but thesame restriction applies.The ID attribute of a document language allows authors to assign anidentifier to one element instance in the document tree. CSS IDselectors match an element instance based on its identifier. A CSSID selector contains a "#" immediately followed by the IDvalue, which must be an identifier.

ID selectors have a higher specificity than attribute selectors.For example, in HTML, the selector #p123 is more specificthan [id=p123] in terms of the cascade.Note. In XML 1.0 [XML10], the information about whichattribute contains an element's IDs is contained in a DTD. Whenparsing XML, UAs do not always read the DTD, and thus may not knowwhat the ID of an element is. If a style sheet designer knows orsuspects that this will be the case, he should use normal attributeselectors instead: [name=p371] instead of#p371. However, the cascading order of normal attributeselectors is different from ID selectors. It may be necessary to addan "!important" priority to the declarations: [name=p371]{color: red ! important}.If an element has multiple ID attributes, all of them must betreated as IDs for that element for the purposes of the IDselector. Such a situation could be reached using mixtures of xml:id[XMLID], DOM3 Core [DOM-LEVEL-3-CORE], XML DTDs [XML10] andnamespace-specific knowledge.5.10 Pseudo-elements and pseudo-classesIn CSS 2.1, style is normally attached to an element based on itsposition in the document tree. Thissimple model is sufficient for many cases, but some common publishingscenarios may not be possible due to the structure of the document tree. For instance, in HTML4 (see [HTML4]), no element refers to the first line of aparagraph, and therefore no simple CSS selector may refer to it.

Neither pseudo-elements nor pseudo-classes appear in the documentsource or document tree.Pseudo-classes are allowed anywhere in selectors whilepseudo-elements may only be appended after the last simple selector ofthe selector.

UAs may return a visited link to the (unvisited) ':link' state atsome point.The two states are mutually exclusive.The document language determines which elements are hyperlinksource anchors. For example, in HTML4, the link pseudo-classesapply to A elements with an "href" attribute. Thus, the followingtwo CSS 2.1 declarations have similar effect:

An element may match several pseudo-classes at the same time.CSS does not define which elements may be in the above states, orhow the states are entered and left. Scripting may change whetherelements react to user events or not, and different devices and UAsmay have different ways of pointing to, or activating elements.CSS 2.1 does not define if the parent of an element that is':active' or ':hover' is also in that state.User agents are not required to reflow a currently displayeddocument due to pseudo-class transitions. For instance, a style sheetmay specify that the 'font-size' of an :active linkshould be larger than that of an inactive link, but since this maycause letters to change position when the reader selects the link, aUA may ignore the corresponding style rule. 2351a5e196